Can PC videogames hurt your computer when played online?

I am pretty sure that games that are streamed from the internet (eg. Runescape, Maplestory, etc. and downloadable demos) can give your computer viruses. But can CD installed games that (when played online) run on a tried-and-true, company run server (like Battle.net) give you viruses or in any other way hurt your PC? Is there any difference between first-party servers (like Battle.net that is run by Blizzard) or third-party servers (like Gamespy) in this issue?

get a fire wall or somekind of wall gamespy is the online thing for the pc it may give it a virus. if you have protection it wont i always play them online and it blocks it but i still play it i just inore it if you put a 360 controller in it will be on xbox live and you basicly have a 360. the 360 is the same thing as the pc you must have a very good computer get xbox live and it wont do anything!!! good luck

The only things I would trust, are game demos hosted by a company. Disk-Downloadable games or games found on a page like Runescape are Risk-Free.

Edit: Battle.net is safe. Just used to connect through the internet for games like starcraft. (Amazing game)