As you are a gamer Linux can't help you now!! There is a very low chance that Steam will come to linux. Interfere with background update means problem with firewall or in AV profile. You can try clam av or BitDefender Free Edition. Both has a av scanner only, you can have a manual update and scan. For real time behavior base protection try threatfire.
I think you are a power user, you don't need a bolted AV, few tools and You can deal with virus.