The John Hopoate Virus Computer will insert random digits - often where they are quite unwanted. Once affected, your computer will no longer accept commands. In some cases, computer will do exact opposite of each command it is given. Will also suddenly disconnect while in the middle of communicating. The end task button works, but nothing else.
Computer seems permanently sluggish.
Start up in the morning can take hours. The Viagra Virus Computer will turn itself on at inappropriate times. Users report difficulty ever turning the damn thing off. The Bureaucrat Virus Constantly reorganises all the files on your computer's desktop, then finds itself unable to actually open any of them. The Heritage Campaigner Virus Saves everything, even your ghastly mistakes.