I've been playing this game on and off for a few years, but I've never had the problem with thiefs. I just logged on, and this random dude was running around on my farm stealing everything he could pick up. Me and my brother kept following him, pushing him around intill he started punching back. We took out our bows and stuff, but he knocked my brother out and stole all his stuff. From what I could tell, it's a guy how just spawn in, unlocks criminal acts, and start stealing what he can come over.
So now is my question. How do you deal with people like this?