Actually PunkBuster is not a virus, and not a DRM tool like Securom. It was designed to prevent cheating in online multiplayer games. It has nothing to do with malware and avast! and you can usually opt out if you don't want to install it. A bunch of installer provide you the option to do so, and it's not required to install it, if you don't plan to play online. There are servers that are not PunkBuster secured, and you can join those servers without any issue if you don't have the stuff installed. Here's what wikipedia says about PunkBuster for you:
PunkBuster is a computer program that is designed to detect software used for cheating in online games. It does this by scanning the memory contents of the local machine. A computer identified as using cheats may be banned from connecting to protected servers. The aim of the program is to isolate cheaters and prevent them from disrupting legitimate games.
The DRM part you are talking about is
Securom, and you can't do much about it. If you bough the game legally you shouldn't panic, because there are nothing to worry about. The benefit of playing legit copies of the game is that you can play online. Pirated copies doesn't allow you to do that, because those games have copy protection removed from the games and you can't even evade the server checks. If you don't have a legit product key from the game and a bogous unprotected executable you can't play the multiplayer mode.
Please pay attention to what the installer tells you, and don't use the
typical option. Sometimes it's a checkbox and sometimes it can be a Yes/No dialog option. If PunkBuster still manages to get on your machine, just simply remove it from the
Control Panel. That will take care of your problem, I guess...
