Jerusalem's most fearsome variant came from Asia. Called Invader, this bug first appeared in Taiwan in July 1990, where it is presumed to have been written. Within a month it had swept through the Far East and was reported to have reached North America. Just four months later it was found at the Canadian Computer Show, where it was running amok on the PC displays. Invader is an exceptionally sophisticated variant. It would infect a target computer's hard disk, diskettes, and program files, and its payload was devastating: it would zap data stored on a hard disk or diskette to the sound of an exploding bomb whenever a particular, quite common, piece of drafting software, called Autocad, was loaded.
Invader is part of the new generation of viruses: destructive, malicious, and clever. Since 1988, as the number of bugs has grown exponentially, virus techniques have improved dramatically, and their infection strategies have become more effective, which means they have a better chance of traveling. They exploit obscure functions of computers in order to evade detection; they can trash data; and in some cases, they can zero out large-scale computer networks.
While the early viruses could cause damage, it was generally by accident; the new strains are programmed to be destructive. Some seem demonic and frenzied, as if the virus writer was driven by a personal animus.
On January 15, 1991, the principal bank on the Mediterranean island of Malta was attacked by a particularly vicious bug. The first warning of the virus was an announcement that popped up suddenly on the computer screen:
DISK DESTROYER--A SOUVENIR OF MALTA I HAVE JUST DESTROYED THE FAT ON YOUR DISK!!
HOWEVER, I HAVE KEPT A COPY IN RAM, AND IM GIVING YOU
A LAST CHANCE TO RESTORE YOUR PRECIOUS DATA.
WARNING: IF YOU RESET NOW ALL YOUR DATA WILL BE LOST FOREVER!! YOUR DATA DEPENDS ON A GAME OF JACKPOT CASINO DE MALTE JACKPOT
+L+~+?+ ~+c+
CREDITS: 5 ANY KEY TO PLAY
The virus was, in essence, inviting operators to gamble with the data on their hard disks. It had captured the FAT, the File Allocation Table which, despite its unprepossessing name, is one of the most important components of a computer's hard disk: it is a master index that keeps track of where all the pages for each file are kept. On a hard disk, unlike in a filing cabinet, pages of a single file are not necessarily stored together; they are stored wherever there happens to be disk space, which often results in "fragmentation"-- particularly of larger files. Whenever a user selects a particular file, the FAT is responsible for finding all of the file's parts and assembling them in the correct order. Once corrupted, the FAT takes on all the attributes of an unqualified temporary secretary: it can't find anything, it loses files, and the ones it doesn't lose are incomplete or presented in the wrong order.
The gamble the operators faced was more or less the same as on a slot machine-- except that the computer user was playing with data instead of a coin. If he played and lost, the virus would zap the FAT, with disastrous consequences. If he played and won, the virus would replace the FAT it had captured with the copy it had sequestered in the RAM, or random access memory, the computer's principal memory, and the area where programs are run.
When the user followed the on-screen instructions and pressed a key, the characters in the three "windows" ran through a sequence, like a real slot machine. The operator had five "credits," or tries, and the game ended when three Ls, Cs, or .~s came up. The operator could try again if a combination of characters came up. The jackpot was three Ls. Then the operator would see the following message on his screen: BASTARD! YOURE LUCKY THIS TIME, BUT FOR YOUR OWN SAKE, SWITCH OFF YOUR COMPUTER NOW AND DONT TURN IT ON UNTIL TOMORROW! Three .~s was a loser: the virus would then announce NO FUCKING CHANCE and destroy the FAT. Three Cs, unsportingly, was also a loser: the message was:
HA HA! YOU ASSHOLE, YOUVE LOST: SAY BYE TO YOUR BALLS. Once again, the FAT would be zapped.
