Virus

The virus, a computer program designed to replicate and spread itself without the user's knowledge, has become a stock character in popular culture. In books and movies, computer viruses are the villains of the Internet Age, wreaking unimaginable havoc on computer systems and threatening the future of civilization. However, that popular portrayal is not very accurate. The majority of viruses are relatively harmless, and very few have the destructiveness of their fictional counterparts. But when a malicious virus does strike, it can cause significant damage.

When the first viruses appeared in 1986, their ability to inflict damage was relatively limited. Early viruses were designed to spread either by attaching themselves to an executable program file, such as a game or word processor, or by infecting the boot sector of a disk. At startup, and when disks are first inserted, computers read the disk's boot sector, and a virus can thus be transmitted before a computer's operating system has a chance to load and prevent the virus' transmission. Regardless of how these early viruses are spread, they were designed to affect files on a single computer. Most viruses were harmless, perhaps popping up a message on a particular day; but others would slowly or rapidly alter or delete files, and particularly vicious ones could wipe out an entire file system.

Early viruses could cause great damage to one computer on their own, but the virus had to have human help in order to spread. For the most part, this meant transmission via floppy disks. For example, a user might be typing up a document on a computer that had a virus. When that file was saved to a floppy disk, the boot sector of that floppy might get infected. Then, when that disk was inserted into the drive of another computer, and the boot sector was read, the new computer would pick up the virus. Or someone might create a game with a built-in virus; a user might put that game on a disk to share with a friend, and unknowingly share the virus as well.

The medium of email has become the biggest carrier of computer-virus infections. Boot-sector viruses are still transmitted by floppy disks, but most other viruses are spread via email attachments. The growth of email as a medium for communication has also led to a phenomenal growth in viruses. From December 1998 to October 1999, for example, the number of known viruses more than doubled, jumping from 20,500 to 42,000. In early 2001, there were over 52,000 known viruses.

Email has also helped foster several new types of malicious programs. A Trojan horse program is an executable file that does something that the user doesn't expect, such as deleting files, but it doesn't replicate itself. For a while, only executable files (programs) could spread viruses, so users could protect themselves by simply not running programs attached to email messages that they received. But with the invention of macro viruses, text documents could also be used to spread viruses. Macros are a series of commands that can be recorded in a word processor or spreadsheet and included in the document file. Since they [Page 474]are in essence small programs, they can be set up to delete files or otherwise damage a system. Most macro viruses target Microsoft's suite of office programs (Word, Excel, Outlook, and so on), since they are so widely used and the programming language of their macros is relatively basic.

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