using NOD32 ESS now, it go easy on my aging rig

The main principle in threatfire is prevention. Based on their mass storage of community protection database, your computer will be protected from various spyware or trojan from penetrate, which whitelist or blacklist is determined from. And there's also on-demand scan for rootkit, and to run "on-demand virus scan"...

So far I'm using it, there's no complain and yet already prevent a trojan from installing bassmode.dll to my system32 folder. Quite impressive but not as good as real HIPS protection + the database...