Most people are aware of threats to their computers. Viruses, Worms and Trojans have become so common that new stories about computer threats appear daily in newspapers and on television. However, what you may not realise is that these threats are relatively new. Two things have happened in recent years to make computer threats possible: computers became affordable and therefore common and the Internet allowed computers to connect easily to each other.
A complete timeline of the history of computer threats can be found on Wikipedia but it is generally accepted that the first major threat was the Morris worm. This software was the first to copy itself from computer to computer, infecting all the machines it came in contact with.
Some people think that only PCs (IBM clones) are at threat and that Apple Macintosh (Mac) and Unix/Linux systems are immune to threats such as viruses. This is not entirely true. Other computers systems are often more secure than PCs. However, the main reason that more PCs are affected by viruses is simply that there are more PCs in the world.
In this course we will concentrate on PC viruses, although a lot of the information supplied will also apply to other systems. As Macs and Linux machines become more common it is likely that they will be threatened by more viruses, as reported in the following article about Macintosh security or in this history of Linux viruses.
The words Trojan, worm and virus are often used interchangeably, but they are not the same. They are all malicious programs (sometimes called “malware”) that can harm your computer, but there are important differences among them, as we will see shortly.