Before widespread use of the Internet, computer viruses were not a common occurrence. Viruses could only be transferred via floppy disk, which meant that it was quite easy to guard against them by simply scanning floppies with anti-virus software. Since files were physically transferred around the world, it could take weeks for a virus to spread, by which time the antidote could be widely distributed, rendering the virus harmless.

With the Internet, however, viruses can travel the world within seconds and become widespread within hours. As the Anna Kournikova and Melissa virus outbreaks have shown, no-one is safe from the effect of viruses. Although the viruses themselves may not be destructive, they can quite easily overload mail servers and Internet gateways, effectively denying access to legitimate messages.

One of the darker sides of the Internet, is that it makes it easier to write and distribute viruses. Lurking around the warez and cracker sites are virus toolkits that contain zoos of active viruses, source code and step-by-step instructions that allow programmers to take revenge on the computer world.

Initially, viruses only lurked in executable programs and floppy boot blocks, whereas nowadays viruses can be embedded in almost any type of code. Word documents, Excel spreadsheets, VBScript, ActiveX controls, screen savers and even email messages themselves can contain virus code. You can catch a virus simply by opening an email attachment or even browsing the Web. This means that for a virus checker to be effective it must filter and validate everything downloaded from the Internet or corporate LAN as well as checking every open file, pre-scanning removable media and checking all downloadable components of Web pages. Since new viruses are released every few minutes, it is no longer possible to wait for the monthly anti-virus updates to arrive in the mail. Good virus checkers should be able to be updated automatically via the Internet and should be able to detect virus-like activity to detect new viruses as they are released.

Editor: Tim Dean
Labs Manager: Ashok Zaman
Contributors: David Neiger