Sam got a popup from what claims to be the FBI requiring him to buy a Moneypak card to get rid of it. It's a scam, malware (more specifically called ransomware) on Sam's system designed to blackmail him into sending them money. He can restart in safe mode and run his antivirus software to clear it. Norton and McAfee both have removal tools for it, too. Even if he clears that off his system, there could be other stuff that has been installed as well, though. So at this point, it's just best to backup his data, format the hard drive and re-install from a known, good source.
Ashar in the chat room says that BleepingComputer.com is a great resource to look up these things.