What Can a Virus Do? It can wipe out entire networks, destroy your computer hard drive, mangle data files (think of all those hours you spent inputting your family history!), and give you a major headache. Viruses can be found on all computer platforms, but luckily there are as many (and hopefully more) good guy anti-virus programmers out there as the evil virus authors. There are two basic types of viruses: boot viruses and file viruses. Boot viruses are run by executable (.exe or .com) files and exist in a small amount of code. File viruses attach themselves to literally any type of file. Boot and file viruses are further described by the terms stealth (they hide by maintaining a set of duplicate files of the ones they corrupt), encrypted (difficult to find because they must be decoded to be recognized), and mutating (polymorphic--they mutate every time they reproduce so their code will be different every time). Anything new (CD, disk, file) entering your system has the potential to contain a virus. There have been cases where commercial software has inadvertantly contained viruses, although this is very rare to the point of being almost unheard of. Generally viruses now come from files downloaded off of Internet, files attached to e-mails, or from a floppy disk (think safe sex for your computer--never share a floppy disk without first scanning it for a virus). The worst part about "catching" a computer virus is that you may not know you've been infected until you notice such things as your system crashing often, sudden memory loss (of your computer, not yours!), inability to access your hard drive, files randomly deleted or significantly changed, and in general a change in how your computer performs. While these symptoms do not mean you have a virus, if you are experiencing one or more, you should scan for viruses.