I came across this story a while ago, and it's been on my "To Share" list for quite some time. It's an article about a guy who was contacted by a scammer, and he knew it was a scammer. He decided to turn the tables on the bad guy, and hilarity ensued.
The basics were simple. The scammer's goal is to get the scammee to download software that will let the scammer take control of his computer. To do this, the scammer argues that the computer is full of viruses, and it needs to be cleaned remotely. The sad news is that this works an awful lot of the time. So many people really don't understand how their computer functions, and they can be suckered into turning the keys to it over to the Wrong Sort of People.
Of course, in this case, the scammee was a techie, and he managed to keep the scammer on the phone for two hours, with lines like "I have to connect to CompuServ" and by playing modem sounds into the phone. I found this incredibly amusing, although I don't think I'd have the patience to stick with something like that for two hours.
The bottom line is that if you have something go wrong with your computer, you call someone to fix it. People don't call you. If anyone ever calls you saying they know your computer is infected or broken, they're either psychic or lying. (Or they're from your work's IT department, I suppose. This doesn't mean their not psychic of lying, of course.) Be very cautious of situations like that.
But that all goes without saying, right?