Your computer becomes obsessed with marrying its own motherboard. Your PC stops every few minutes to ask for money. Your computer gets fat, slow, and lazy and then self destructs, only to resurface at shopping malls and service stations across rural America. Turns your printer into a document shredder. Your data won't appear unless you buy new cables, power supply, and a set of shocks.
Nobody can find it.
Runs every program on the hard drive simultaneously, but doesn't allow the user to accomplish anything. Helps your computer shut down whenever it wants to. Invades your system in places where no virus has gone before. Your PC makes frequent mistakes and comes in last in the reviews, but you still love it.