I occasionally play with a guy who hasn't bought the second map pack yet. Somehow, the previous packs are loaded with hackers.
I found a way around, though! We have about 10 people in our group who have all downloaded a MW2 Server Admin.
We all have pretty good computers, so it's pretty likely that one of us is hosting. Using the program, a person can sever the hacker's connection to the server, kicking him and banning him.
We try not to abuse it. We really do!