A coworker in the office here brought up Cryptolocker this morning. I've heard of it, but never seen it in the wild. It's ransomware that encrypts documents and hits you up for money or deletes them in a couple of day's time. Nasty stuff... Anyways, he stumbled upon a prevention kits of sorts using GPO. I'm only reading through it now, but it looks pretty cool.
Cryptolocker Prevention Kit (updated) - Spiceworks