I don't know the first thing about installing a firewall.
I have a router connecting both a pc and a mac to the adsl ( I don't if this is relevant...)
I have just rebooted my pc after having run all scans by Avast and Adaware, and I don't hear that terrible warning that I am infected, so maybe I'm fine.
Do trojans all do the same thing? I thought some were more harmful than others... I guess I'm just too old for this stuff...