I fix computers at a local shop. People come in all the time with the FBI Virus on their computer
Basically, it's a scam. But recently we have gotten a few people who have come in that actually believe the FBI is watching them (because the virus shows their webcam feed on the screen if they have one) and have sent money in as part of the scam! People ask if we can help them get their money back and we basically tell them "Sorry, you're fucked, call the credit card company!"
Funny thing is, this virus takes all of 5 minutes to remove!