In 1987, the University of Delaware realised that they had this virus, when they started seeing the label " (c) Brain" on floppy diskettes. That's all it did - copy itself, and put a volume label on diskettes.
Meanwhile, also in 1986, a programmer called Ralf Burger realised that a file could be made to copy itself, by attaching a copy of itself to other files. He wrote a demonstration of this effect, which he called VIRDEM. He distributed it at the Chaos Computer Club conference that December, where the theme was viruses. VIRDEM would infect any COM file; again the payload was pretty harmless.
This attracted so much interest, that he was asked to write a book. Ralf hadn't thought of boot sector viruses like Brain, so his book doesn't even mention them. But by then, someone had started spreading a virus, in Vienna.
In 1987, Franz Swoboda became aware that a virus was being spread in a program called Charlie. He called it the Charlie virus. He made lots of noise about the virus (and got badly bitten as a result). At this point, there are two versions of the story - Burger claims that he got a copy of this virus from Swoboda, but Swoboda denies this. In any case, Burger obtained a copy, and gave it to Berdt Fix, who disassembled it (this was the first time anyone had disassembled a virus). Burger included the disassembly in his book, after patching out a couple of areas to make it less infectious and changing the payload. The normal payload of Vienna is to cause one file in eight to reboot the computer (the virus patches the first five bytes of the code); Burger (or maybe Fix) replaced this reboot code with five spaces. The effect was that patched files hung the computer, instead of rebooting. This isn't really an improvement.
Meanwhile, in the US, Fred Cohen had completed his doctoral dissertation, which was on computer viruses. Dr. Cohen proved that you cannot write a program that can, with 100% certainty, look at a file and decide whether it is a virus. Of course, no one ever thought that you could, but Cohen made good use of an existing mathematical theorem and earned a doctorate. He also did some experiments; he released a virus on a system, and discovered that it travelled further and faster than anyone had expected.
In 1987, Cohen was at Lehigh, as was Ken van Wyk. So was the author of the Lehigh virus. Lehigh was an extremely unsuccessful virus - it never managed to spread outside its home university, because it could only infect COMMAND.COM and did a lot of damage to its host after only four replications. One of the rules of the virus is that a virus that quickly damages it host, cannot survive. However, the Lehigh virus got a lot of publicity, and led to van Wyk setting up the Virus-L newsgroup on Usenet. Lehigh was nasty. After four replications, it did an overwrite on the disk, hitting most of the File Allocation Table. But a virus that only infects COMMAND.COM, isn't very infectious.
Meanwhile, in Tel Aviv, Israel (some say in Italy), another programmer was experimenting. His first virus was called Suriv-01 (virus spelled backwards). It was a memory resident virus, but it could infect any COM file, whereas Lehigh could only infect COMMAND.COM. This is a much better infection strategy than the non-TSR strategy used by Vienna, as it leads to files on all drives and all directories being infected. His second virus was called Suriv-02, and that could infect only EXE files, but it was the first EXE infector in the world. His third attempt was called Suriv-03, and it could handle COM and EXE files. His fourth effort escaped into the world, and became known as Jerusalem virus. Every Friday 13th, instead of infecting files that are run, it deletes them. but Friday 13t are not common, so the virus is pretty inconspicuous, most of the time. It avoids infecting COMMAND.COM, because in those days, many people believed that this was the file to watch (see Lehigh).
It looks as if it escaped rather than was released, because it plainly was not ready for release. The author decided to change the way that the virus detected itself in EXE files, and had made part of that change. There is redundant code from the Suriv viruses still in place, and also what looks like debugging code. It was found in the Hebrew University of Jerusalem (hence the name) by Yisrael Radai.
While all this was going on, a young student at the University of Wellington, New Zealand, had found a very simple way to create a very effective virus. One time in eight, when booting from an infected floppy, it also displayed the message 'Your PC is now Stoned', hence the name of the virus.
The virus itself was just a few hundred bytes long, but because of its selfrestraint, and memory-resident replication, it has become the most widespread virus in the world, accounting for over a quarter of outbreaks. It is very unlikely that Stoned virus will ever become rare. The virus spread rapidly, because of its inconspicuousness (and because in those days, people were keeping a careful eye on COMMAND.COM, because of Lehigh).
In Italy, at the University of Turin, a programmer was writing another boot sector virus. This one put a bouncing ball up on the screen, if the disk was accessed exactly on the half hour. It became known as Italian virus, Ping pong, or Bouncing Ball. But this virus had a major defect - it couldn't work on anything except an 8088 or 8086 computer, because it uses an instruction that doesn't work on more advanced chips. As a result, this virus has almost died out (as has Brain, which can only infect 360 kb floppies, and which foolishly announces its presence via the volume label).
Back in the US, an American was demonstrating a problem that has continued to dog US virus writers ever since - incompetence. The Lehigh didn't make it outside a small circle - neither did the Yale virus. This was another boot sector virus, but it only copied itself when you booted from an infected floppy, then put another floppy in to continue the boot process. No subsequent diskette was infected, and if the boot-up continued from a hard disk, there was no infection at all. Yale never spread at all widely, either.
But also in 1987, a German programmer was writing a very competent virus, the Cascade, so called after the falling letters display that it gave. Cascade used a new idea - most of the virus was encrypted, leaving only a small stub of code in clear for decrypting the rest of the virus. The reason for this was not clear, but it certainly made it more difficult to repair infected files, and it restricted the choice of search string to the first couple of dozen bytes. This idea was later extended by Mark Washburn when he wrote the first polymorphic virus, 1260 (Chameleon). Washburn based Chameleon on a virus that he found in a book - the Vienna, published by Burger.
Cascade was supposed to look at the BIOS, and if it found and IBM copyright, it would refrain from infecting. This part of the code didn't work. The author soon released another version of the virus, 1704 bytes long instead of 1701, in order to correct this bug. But the corrected version had a bug that meant that it still didn't detect IBM BIOSes.
Of these early viruses, only Stoned, Cascade and Jerusalem are common today, but those three are very common.
In some ways, that was a pity, because 1988 was a very virus-friendly year. It gave Stoned, Cascade and Jerusalem a chance to spread undetected, and to establish a pool of infected objects that will ensure that they never become rare.
It was in 1988 that IBM realised that it had to take viruses seriously. This was not because of the well-known Christmas tree worm, which was pretty easy to deal with. It was because IBM had an outbreak of Cascade at the Lehulpe site, and found itself in the embarrassing position of having to inform its customers that they might have become infected there. In fact, there was no real problem, but from this point on, IBM took viruses very seriously indeed, and the High Integrity Computing Laboratory in Yorktown was given responsibility for the IBM research effort in this field.
1988 saw a few scattered, sporadic outbreaks of Brain, Italian, Stoned, Cascade and Jerusalem. It also saw the final arguments about whether viruses existed or not. Peter Norton, in an interview, said that they were an urban legend, like the crocodiles in the New York sewers, and one UK expert claimed that he had a proof that viruses were a figment of the imagination. In 1988, the real virus experts would debate with such people - after that year, real virus experts would simply walk away from anyone who had such absurd beliefs.
Each outbreak of a virus was dealt with on a case-by-case basis. One American claimed that he had a fully equipped mobile home for dealing with virus outbreaks (and another one extrapolated to the notion that soon there would be many such mobile units). Existing software was used to detect boot sector viruses (by inspecting the boot sector), and one-off software was written for dealing with outbreaks of Cascade and Jerusalem.
In 1988, a virus that is called "Virus-B" was written. This is another virus that doesn't go memory resident, and it is a modification of another virus that deletes files on Friday 13th. When this virus is run, it displays "WARNING!!!! THIS PROGRAM IS INFECTED WITH VIRUS-B! IT WILL INFECT EVERY .COM FILE IN THE CURRENT SUBDIRECTORY!". A virus that is as obvious as that, was clearly not written to spread. It was obviously written as a demonstration virus. Virus researchers are often asked for "harmless viruses" or "viruses for demonstration"; most researchers offer some alternative, such as an overhead foil, or a non-virus program that does a falling letters display. But it looks as if VIRUS-B was written with the intention of giving it away as a demonstration virus - hence the warning. And, indeed, we find that an American company was offering it to "large corporations, universities and research organizations" on a special access basis.
At the end of 1988, a few things happened almost at once. The first was a big outbreak of Jerusalem at a large financial institution, which meant that dozens of people were tied up in doing a big clean-up for several days. The second was that a company called S&S did the first ever Virus Seminar that actually explained what a virus was and how they worked. The third was Friday 13th.
It was clear that we couldn't go out and help everyone with a virus, even if we bought a mobile home and equipped it (with what)? It was also clear that the financial institution, and the academic site, could easily handle a virus outbreak, but they didn't have the tools to do the job. All they needed was a decent virus detector, which was not available. So we wrote one, added some other tools that experience said might be useful, and created the first Anti Virus Toolkit.
In 1989, the first Friday 13th was in January. At the end of 1988, it was clear that Jerusalem was in Spain and the UK, at least, and was in academic as well as commercial sites. Because of the destructive payload in the virus, we felt that if we failed to send out some sort of warning, we would be negligent. But the media grabbed the ball and ran with it; the predictability of the trigger day, together with the feature of it being Friday 13th, caught their imagination, and the first virus media circus was under way.
On the 13th of January, we had dozens of phone calls, mostly from the media wanting to know if the world had ended yet. But we also had calls from a large corporate site, a small vendor of PC hardware, and a couple of single users. We were invaded by TV cameras in droves, and had to schedule them carefully to avoid them tripping over each other. In the middle of all this, the PC Support person from the infected corporate arrived. The TV people wanted nothing better than a victim to film, but the corporate wanted anonymity. We pretended that he was just one of our staff. Also, at that time, British Rail contacted us - they also had an outbreak of Jerusalem, and they went public on it. Later, they regretted that decision, because for a long time afterwards, their PC Support person was badgered by the media seeking interviews.
In March of 1989, a minor event happened that was to trigger an avalanche. A new virus was written in Holland. A Dutchman calling himself Fred Vogel (a very common Dutch name) contacted a UK virus researcher, and said that he had found this virus all over his hard disk. He also said that it was called Datacrime, and that he was worried that it would trigger on the 13th of the next month.
When the virus was disassembled, it was found that on any day after October 12th, it would trigger a low level format of cylinder zero of the hard disk, which would, on most hard disks, wipe out the File Allocation Table, and leave the user effectively without any data. It would also display the virus's name, Datacrime virus. A straightforward write-up of the effect of this virus was published, but it was another non-memory-resident virus, and so highly unlikely to spread.
However, the write-up was reprinted by a magazine, another magazine repeated the story, a third party embellished it a bit, and by June it was becoming an established fact that it would trigger on October 12th (not true, it triggers on any day after the 12th, up till December 31st) and that it would low level format the whole hard disk. In America, the press started calling it "Columbus Day virus" (October 12th) and it was suggested that it had been written by Norwegian terrorists, angry at the fact that Eric the Red had discovered America, not Columbus.
Meanwhile, in Holland, the Dutch police were doing one of the things that falls within those things that police are supposed to do - crime prevention. Datacrime virus was obviously a crime, and the way to prevent it was to run a detector for it. So the commissioned a programmer to write a Datacrime detector, and offered it at Dutch police stations for $1. It sold really well. But it gave a number of false alarms, and it had to be recalled, and replaced with version 2. There were long queues outside the Dutch police stations, lots of confusion about whether anyone actually had this virus (hardly anyone did, but the false alarms muddied the waters).
If the police take something seriously, it must be serious, right? So in July, large Dutch companies started asking IBM if viruses were a serious threat. Datacrime isn't, but there is a distinct possibility that a company could get Jerusalem, Cascade or Stoned (or Italian, in those days before 8088 computers became a rarity). So what is IBM doing about this threat, they asked?
IBM had internal-use-only anti-virus software. They used this to check incoming media, and to make sure that an accident like Lehulpe could never happen again. IBM had a problem - if they didn't offer this software to their customers, they could look very bad if on October 13th a lot of computers went down. The technical people knew that this wouldn't happen, but obviously they knew that someone, somewhere, might have important data on a computer that would get hit by Datacrime. IBM had to make a decision about whether to release their software, and they had a very strict deadline to work to - October the 13th would be too late.
In September of 1989, IBM sent out version 1.0 of the IBM scanning software, together with a letter telling their customers what it was, and why they were sending it out. When you get a letter like that from IBM, and a disk, you would be pretty brave to take no notice, so a lot of large companies scanned a lot of computers, for the first time. Hardly anyone found Datacrime, but there were instances of the usual viruses.
October 13th fell on a Friday, so there was a double event - Jerusalem and Datacrime. In the US, Datacrime (Columbus Day) had been hyped out of all proportion for a virus that is as uninfective as this one, and it is highly likely that not a single user had the virus. In Europe (especially in Holland) there might have been a few, but not many.
In London, the Royal National Institute for the Blind announced that they'd had a hit, and had lost large amounts of valuable research data, and months of work. We investigated this particular incident, and the truth was that they had a very minor outbreak of Jerusalem, and a few easily-replaced program files had been deleted. Four computers were infected. But the RNIB outbreak has passed into legend as a Great Disaster. Actually, the RNIB took more damage from the invasion of the television and print media than from the virus.
By the end of 1989, there were a couple of dozen viruses that we knew about, but we didn't know that in Bulgaria and Russia, big things were brewing.
One consequence of this, was that some vendors couldn't do this. It isn't easy to write such an algorithm, and many vendors were, by this time, relying on search strings extracted by someone else. The three main sources of search strings were a newsletter called Virus Bulletin, the IBM scanner, and reverse engineering a competitor's product. But you can't detect a polymorphic virus this way (indeed, two years after these viruses were published, many products are still incapable of detecting these viruses). Washburn also published his source code, which is now widely available. At the time, we thought that this would bring out a number of imitators; in practice, no-one seems to be using Washburn's code. However, plenty of virus authors are using his idea.
Another consequence of polymorphic viruses, was an increase in the false alarm rate. If you write code to detect something that has as many possibilities as V2P6, then there is a chance that you will flag an innocent file, and that chance is much greater than with the sort of virus that you can find with a 24-byte scan string. A false alarm can be as much hassle to the user as a real virus, as he will put all his anti-virus procedures into action.
Also, in 1990, we saw a number of virus coming out of Bulgaria, especially from someone who called himself "Dark Avenger". The Dark Avenger viruses introduced two new ideas. The first idea was the "fast infector"; with these viruses, if the virus is in memory, then simply opening a file for reading, triggers the virus infection. The entire hard disk is very soon infected. The second idea in this virus, was that of subtle damage. Dark Avenger-1800 occasionally overwrites a sector on the hard disk. If this isn't noticed for a period of time, the corrupted files are backed up, and when the backup is restored, the data is still no good. Dark Avenger targets backups, not just data. Other viruses came from the same source, such as the Number-of-the-Beast (stealth in a file virus) and Nomenklatura (with an even nastier payload than Dark Avenger.
Also, Dark Avenger was more creative about distributing his viruses. He would upload them to BBSes, infecting shareware anti-virus programs, together with a documentation file that gave reassurance to anyone who checked the file size and checksums. He uploaded his source code also, so that people could learn how to write viruses.
In 1990, another event happened in Bulgaria - the first virus exchange BBS. The idea was that if you uploaded a virus, you could download a virus, and if you uploaded a new virus, you were given full access. This, of course, encourages the creation of new viruses, and gets viruses into wider circulation. Also, the VX BBS offered source code, which makes the technology of writing a virus more widely available.
In the second half of 1990, The Whale appeared. Whale was a very large, and very complex virus. It didn't do very much; mostly, it crashed the computer when you tried to run it. But it was an exercise in complexity and obfuscation, and it arrived in virus author's hands like a crossword puzzle to be solved. Some virus researchers wasted weeks unravelling Whale, although in practice you could detect it with a couple of dozen search strings, and you didn't really need to do any more, as the thing was too clumsy to work anyway. But because it was so large and complex, it achieved fame.
At the end of 1990, the anti-virus people saw that they had to get more organised - they had to be at least as organised as the virus authors. So EICAR (European Institute for Computer Antivirus Research) was born in Hamburg, in December 1990. This gave a very useful forum for the anti-virus researchers and vendors to meet and exchange ideas (and specimens), and to encourage the authorities to try to prosecute virus authors more vigorously. At the time that EICAR was founded, there were about 150 viruses, and the Bulgarian "Virus Factory" was in full swing.
Glut means lots of viruses, and this causes a number of unpleasant problems. In every program, there must be various limitations. In particular, a scanner has to store search strings in memory, and under DOS, there is only 640 kb to use (and DOS, the network shell and the program's user interface might take half of that).
Another Glut problem, is that some scanners slow down in proportion to the number of viruses scanned for. Not many scanners work this way, but it certainly poses a problem for those that do.
A third Glut problem, comes with the analysis of viruses; this is necessary if you want to detect the virus reliably, to repair it, and if you want to know what it does. If it takes one researcher one day to disassemble one virus, then he can only do 250 per year. If it takes one hour, that figure becomes 2000 per year, but whatever the figure, more viruses means more work.
Glut also means a lot of viruses that are similar to each other. This then can lead to mis-identification, and therefore a wrong repair. Very few scanners attempt a complete virus identification, so this confusion about exactly which virus is being found, is very common.
Most of these viruses came from Eastern Europe and Russia - the Russian virus production was in full swing. But another major source of new viruses was the virus exchange BBSes.
Bulgaria pioneered the VX BBS, but a number of other countries quickly followed. Some shut down not long after they started up, but the Milan "Italian Virus Research Laboratory" was where a virus author called Cracker Jack uploaded his viruses (which were plagiarised versions of the Bulgarian viruses). Germany had Gonorrhea, Sweden had Demoralised Youth, America had Hellpit, UK had Dead On Arrival and Semaj. Some of these have now either closed down or gone underground, but they certainly contributed to the glut problem. With a VX BBS, all a virus author has to do, is download some source code, make a few simple changes, then upload a new virus, which gives him access to all the other viruses on the board.
1991 was also the year that polymorphic viruses first made a major impact on users. Washburn had written 1260 and the V2 series long before, but because these were based on Vienna, they weren't infectious enough to spread. But in April of 1991, Tequila burst upon the world like a comet. It was written in Switzerland, and was not intended to spread. But it was stolen from the author by a friend, who planted it on his father's master disks. Father was a shareware vendor, and soon Tequila was very widespread.
Tequila used full stealth when it installed itself on the partition sector, and in files it used partial stealth, and was fully polymorphic. A full polymorphic virus in one for which no search string can be written down, even if you allow the use of wild cards. Tequila was the first polymorphic virus that was widespread. By May, the first few scanners were detecting it, but it was not until September that all the major scanners could detect it reliably. If you don't detect it reliably, then you miss, say, 1% of infected files. The virus starts another outbreak from these overlooked instances, and has to be put down again, but now there is that old 1%, plus another 1% of files that are infected but not detected. This can continue for as long as the user has patience, until eventually the hard disk contains nothing but files that the scanner cannot detect. The user, thinks that after the virus coming back a number of times, it gradually infected fewer and fewer files, until now he has gotten rid of it completely.
In September 1991, Maltese Amoeba spread through Europe - another polymorphic virus. By the end of the year, there were a few dozen polymorphic viruses. Each of these is classified as "difficult", meaning it takes a virus researcher more than a few hours to do everything that needs to be done. Also, most products need some form of hard coding in order to detect the virus, which means program development, which means bugs, debugging, beta testing and quality control. Furthermore, although a normal virus won't slow down most scanners, a polymorphic virus might.
It was also in 1991, that Dark Avenger announced the first virus vapourware. He threatened a virus that had 4,000,000,000 different forms. In January 1992, this virus appeared, but it wasn't a virus.
This was followed by Dark Avenger's Commander Bomber. Before CB, you could very easily predict where in the file the virus would be. Many products take advantage of this predictability to run fast; some only scan the top and tail of the file, and some just scan the one place in the file that the virus must occupy if it is there at all. Bomber transforms this, and so products either have to scan the entire file, or else they have to be more sophisticated about locating the virus.
Another virus that came out at about that time, was Starship. Starship is a fully polymorphic virus (to defeat scanners), with a few neat anti-debugging tricks, and it also aims to defeat checksummers with a very simple trick. Checksumming programs aim to detect a virus by the fact that it has to change executable code in order to replicate. Starship only infects files as they are copied from the hard disk to the floppy. So files on the hard disk never change. But the copy on the floppy disk is infected, and if you then copy that onto a new hard disk, and tell the checksummer on the new machine about this new file, the checksummer will happily accept it, and never report any changes. Starship also installs itself on the hard disk, but without changing executable code. It changes the partition data, making a new partition as the boot partition. No code is changed, but the new partition contains the virus code, and this is run before it passes control on to the original boot partition.
Probably the greatest event of 1992 was the great Michelangelo scare. One of the American anti-virus vendors forecast that five million computers would go down on March the 6th, and many other US vendors climbed on to the bandwagon. PC users went into a purchasing frenzy, as the media whipped up the hype. On March the 6th, between 5,000 and 10,000 machines went down, and naturally the US vendors that had been hyping the problem put this down to their timely and accurate warning. We'll probably never know how many people had Michelangelo, but certainly in the days leading up to March the 6th, a lot of computers were checked for viruses. After March 6th, there were a lot of discredited experts around.
The reaction to the Michelangelo hype did a lot of damage to the credibility of people advicating sensible antivirus strategies, and outweighed any possible benefits from the gains in awareness.
In August 1992, we saw the first serious virus authoring packages. First the VCL (Virus Creation Laboratory) from Nowhere Man, and then Dark Angel's Phalcon/Skism Mass-Produced Code Generator. These packages made it possible for anyone who could use a computer, to write a virus. Within twelve months, dozens of viruses had been created using these tools.
Towards the end of 1992, a new virus writing group called ARCV (Association of Really Cruel Viruses) had appeared in England - within a couple of months, the Computer Crime Unit of New Scotland Yard had tracked them down and arrested them. ARCV flourished for about three months, during which they wrote a few dozen viruses and attracted a few members.
Another happening of 1992, was the appearance of people selling (or trying to sell) virus collections. To be more precise, these were collections of files, some of which were viruses, and many of which were assorted harmless files. In America, John Buchanan offered his collection of a few thousand files for $100 per copy, and in Europe, The Virus Clinic offered various options from #25. The Virus Clinic was raided by the Computer Crime Unit; John Buchanan is still offering viruses for sale.
Towards the end of 1992, the US Government was offering viruses to people who called the relevant BBS.
Early in 1993, a new virus writing group appeared, in Holland, called Trident. The main Trident author, Masouf Khafir, wrote a polymorphic engine called the Trident Polymorphic Engine, and release a virus that used it, called GIRAFE. This was followed by updated versions of the TPE. The TPE is much more difficult to detect reliably than the MtE, and very difficult to avoid false alarming on.
Khafir also released the first virus that worked according to a principle first described by Fred Cohen. The Cruncher virus was a data compression virus, that automatically added itself to files in order to auto-install on as many computers as possible.
Meanwhile, Nowhere Man, of the Nuke group, had been busy. Early in 1993, he released the Nuke Encryption Device (NED). This was another mutator that was more tricky than MtE. A virus called Itshard soon followed.
Phalcon/Skism was not to be left out. Dark Angel released DAME (Dark Angel's Multiple Encyptor) in an issue of 40hex; a virus called Trigger uses this. Trident released version 1.4 of TPE (again, this is more complex and difficult than previous versions) and released a virus called Bosnia that uses it.
Soon after that, Lucifer Messiah, of Anarkick Systems had taken version 1.4 of the TPE and written a virus POETCODE, using a modified version of this engine (1.4b).
Early in 1993, another highly polymorphic virus appeared, called Tremor. This rocketed to stardom when it got included in a TV broadcast of software (received via a decoder).
In the middle of 1993, Trident got a boost when Dark Ray and John Tardy joined the group. Tardy has released a fully polymorphic virus in 444 bytes, and we can expect more difficult things from Trident.
The main events of 1993, were the emergence of an increasing number of polymorphic engines, which will make it easier and easier to write viruses that scanners find difficult to detect.
The glut problem will continue, and could get sharply worse. Whenever a group of serious anti-virus researchers meet, we find an empty room, hang "Closed for cleaning" on the door, and frighten each other with "nightmare scenarios". Some of the older nightmare scenarios have already come true, others have not, but remain possibilities. The biggest nightmare for all anti-virus people is glut. There are only about 10-15 first class anti-virus people in the world, and most of the anti-virus companies have just one of these people (some have none). It would be difficult to create more, as the learning curve is very steep. The first time you disassemble something like Jerusalem virus, it takes a week. After you've done a few hundred viruses, you could whip through something as simple as Jerusalem in 15 minutes.
The polymorphic viruses will get more numerous. It turns out that they are a much bigger problem than the stealth viruses, because stealth is aimed at checksummers, but polymorphism is aimed at scanners, which is what most people are using. And each polymorphic virus will be a source of false alarms, and will cause the researchers much more work than the normal viruses.
The polymorphic viruses will also continue to get more complex, as virus authors learn the technique, and increasingly try to ensure that their viruses cannot be detected.
Scanners will get larger - more code will be needed because more viruses will need hard coding to scan for them. The databases that scanners use will get larger; each new virus needs to be detected, identified and repaired. Loading the databases will take longer, and some programs will have memory shortage problems.
As Windows becomes more popular, people will be increasingly reluctant to run scanners under DOS. But if you are running Windows, you have run software on the hard disk, and if one of the things you've run is infected by a virus, you have a virus in memory. If there is a virus in memory, you cannot trust what the computer is saying - it could be a stealth virus. Windows will make antivirus software less secure.
The R&D effort to keep scanners up-to-date will get more and more. Some companies won't be able to do it, and will decide that scanning is outdated technology, and try to rely on checksumming. Other companies will licence scanners from one of the few companies that still maintains adequate R&D (we've already started seeing some of this). Some companies will decide that the anti-virus business isn't as profitable as they had thought, and will abandon their anti-virus product, and go back to their core business.
Users will get a lot more relaxed about viruses. We've long since passed the stage where a virus is regarded as a loathsome disease, to be kept secret. But we're increasingly seeing people who regard a virus on their system with about the same degree of casualness as a bit of fluff on their jacket. Sure, they'll wipe it off, but there's not real need to worry about it happening again. This is perhaps a bit too relaxed an attitude, but what can you expect if a user keeps on getting hit by viruses, and nothing terrible ever seems to result.
Anti-virus products will mature a lot. Those without any kind of decent user interface will have a hard time competing against the pretty ones. Those with a long run time will be rejected in favour of those that run in seconds. Exactly which viruses are detected will have far less emphasis (it is very difficult for users to swallow claims about so many thousands of viruses) than the ease of use of the product, and the amount of impact it has on the usability of the computer.
New products will keep arriving, as each company invents the product that makes all previous products obsolete. Sometimes the magic ingredient will be software (AI, neural nets, whatever is the latest buzzword) and sometimes it will be hardware (which can never be infected, except that that isn't the problem). These products will burst on a startled world in a blaze of publicity, and vanish without trace when users find that installing them makes their computer unusable, or else it doesn't find any viruses, or both. But new ones will come along to take their place.
Gradually, people will trade up from DOS to whatever takes its place - OS/2, Windows-NT or Unix, and the DOS virus will become as irrelevant as CPM. Except that DOS will still be around 10 or even 20 years from now, and viruses for the new operating system will start to appear as soon as it is worth writing them.
Some computers are already being built with ingrained resistance to viruses. Some brands of computer are already immune to boot sector viruses, provided you make a simple choice in the CMOS setup (don't boot from the floppy). Right now, very few users are being told that these computers can be set up that way, but people are gradually finding out for themselves. This doesn't solve the virus problem, but anything that makes the world a difficult place for viruses must be a help.
The virus problem will be with us for ever. It isn't the dramatic, worldshaking kind of problem that Michelangelo was made out to be; nor is it the fluff-on-your-jacket kind of problem. But as long as people have problems with computers, other people will be offering solutions for those problems.