Malware: Computing's Dirty Dozen

It seems that no sooner do you feel safe turning on your computer than you hear on the news about a new kind of internet security threat. Usually, the security threat is some kind of malware (though the term "security threat" no doubt sells more newspapers).
What is malware? Malware is exactly what its name implies: mal (meaning bad, in the sense of malignant or malicious rather than just poorly done) ware (short for software). More specifically, malware is software that does not benefit the computer's owner, and may even harm it, and so is purely parasitic.
The Many Faces of Malware
According to Wikipedia, there are in fact eleven distinct types of malware, and even more sub-types of each.
1. Viruses. The malware that's on the news so much, even your View the rest of this article