"Be careful and do not turn on your computer tomorrow, or a computer virus will activate". Everybody has listened to these words since the 90s. In fact some friends of mine didn’t actually use their computers on those days. I personally preferred to take the risk and avoid watching telly. I know doing my homework would be better, but… I just loved computers!

A computer virus is a piece of malicious code. Let’s take a look at its anatomy:

  • Replication: It must be able to infect other computers.
  • Keeping hidden: The final user doesn’t have to know about its existence.
  • Reach an objective: Just for fun, spying, making money...

That’s why they are called viruses, for their similarity with biological viruses. The concept of computer virus is ages old. John von Neumann published an article in 1949 called "Theory of self-reproducing automata". Michael Crichton, known for many good science-fiction books like Jurassic Park, made an early mention on the concept of computer viruses in his movie "Westworld" (1973).

The very first computer virus was written in a laboratory in 1971 by Bob Thomas to test self-replication. That was precisely what that virus did, replicate itself and infected other computers and showed the following message:

"I’m the creeper, catch me if you can!" However this virus was harmless, so no damage was caused. The creator named it "The Creeper" and, as it was the first virus there were no antivirus software was available yet. However, "The Reaper" program was the first antivirus later created to counteract Creeper.

The Rabbit virus appeared in 1974 with the only purpose of replicating itself unlimited times until all resources were spent in the host machine. This kind of attack is known as a fork bomb.

1981, Rich Skrenta, a 15 year old high-school student, wrote a virus called "The Cloner" to annoy his school friends. The virus became famous when it infected multiple computers, so it propagated really quick for those times. The propagation was slower than it happens today, due to the infection being spread via floppy disks. . One funny thing about this one is its behavior. After 50 boots, when it happened it shows this text on screen:

The Cloner: The program with a personality It will get on all your disks It will infiltrate your chips Yes it's Cloner! It will stick to you like glue It will modify RAM too Send in the Cloner!

Despite this piece of literature, this virus was not designed to perform any damage, just to be a pain, however as it didn’t take any care when manipulating operating system records, it could corrupt the OS and damage systems. That was really annoying about the virus! Congrats Rich! You made it!

Does anybody of you know the "Brain" virus? It was written in 1986 for a couple of Pakistani brothers, and it’s famous to be the first virus to infect an IBM PC compatible. Brain was a celebrity too, as it was in the papers and the society was informed about it. The Amjad brothers run a computer shop, "Brain Computer Services", where they sold the software they developed, and, what did they do to protect their software from piracy? Exactly, they created "Brain".

The virus really didn’t want to harm any personal data, but sometimes it could happen. The virus just dropped a kind of business card that displayed a message similar to this: "Welcome to the Dungeon ... (c) 1986 Brain & Amjads (pvt) Ltd ... 430791.443248.280530 VIRUS_SHOE RECORD V9.0 ... Dedicated to the dynamic memories of millions of virus who are no longer with us today - Thanks GOODNESS !! ... BEWARE OF THE er ... VIRUS..."

Jerusalem is a very famous virus too, also known as Friday 13th, appeared one year later, on 1987. This virus used to infect .EXE and .COM files exclusively and was installed itself on the RAM memory of the host machine. This virus was really lethal, as it removes all executable files upon every occurrence of Friday the 13th. It caused a worldwide epidemic in 1988.

It was detected in city of Jerusalem, that’s why it’s known as such, and it happened due to a failure on its programming logic. The Jerusalem virus didn’t check a file before infecting, so it could infect the already-infected-files many times. Every time its size increased by 2Kb, not too much for the computers we use today, but a lot for those old computers. At some point the virus forced a deny of service for the lack of resources in the operating system.

If you think Jerusalem was bad, listen to this one called Michelangelo. It expected to create an apocalypse on the 6th March 1992, with millions of computers infected that would lose absolutely all their data, or at least that was the mass media published. Michelangelo infects the master boot record every time the system uses an infected floppy disk, and infects all floppies and hard disks from there. Seems like the viruses have passed from laughs to tears, becoming more lethal and malicious every time.

Viruses became harder to detect by antiviruses when polymorphic computer viruses appeared: some examples of this kind of virus are "Pogue" and "Coffeeshop" – both from the "Dark Avenger Mutation Engine", and "OneHalf".

Year 1995 brought one of the most famous products from Microsoft: Windows 95. Our screens become full of colors and windows, instead of those black command line screen from MS-DOS. The new operating system brings new viruses too!

In 1996 the first Macro virus was created with the name "World Concept". This virus wrote this phrase: "That’s enough to prove my point" in Microsoft Word. So far, virus development required a good knowledge of operating system programming and communications; however, "World Concept" could be written with just minimal knowledge. "Laroux" appears this year too, the first macro virus for Microsoft Excel.

So far the ROM BIOS content was inviolable, so far… because CIH/Chernobyl virus appears with the malicious purpose of erasing your ROM BIOS content. That was bad… reinstalling an OS was not enough to fix the problem, because the virus was now able to modify software on the motherboard. That piece of malicious code was written for Windows9X in 1998 by Chen Ing Hau, or CIH for short, the same acronym that named the virus. The author chose the 26th April for its activation to celebrate his birthday. However the Chernobyl disaster happened on the same date and that’s why it is also known as Chernobyl virus, which is a proper name for a devastating computer virus.

We are almost finished with the the century! Every year the viruses were more complicated, dreadful and propagate faster thanks to the Internet. In 1999 some worms appeared: "Happy99", "ExploreZip", "Kak worm" and "Melissa worm". This last one became really popular among email users. Melissa was not really devastating, it only replicated unlimited and saturates those inboxes with SPAM!! SPAM!! SPAM!!

I know the XXI century lasts until 2000 and arrives with a classic virus that spread love everywhere, called "I love you", but we better leave it for a next post about modern viruses. Don’t miss it!

Keep it secure!