I think what is more relevant is the likely means of delivery, from your link.
While SpySweeper suggests that the Poison Ivy trojan is normally spread via email attachment, one of the first reports of PoisonIvy.20.A detection was an infected Runescape (online multiplayer game) hack posted on a gaming message board, and shortly afterwards a similarly posted Diablo II hack was also found infected with the same. It seems that many of the Firefox users affected by the symptoms admit to playing other online multiplayer games - giving some credence to the idea that infected game hacks(cheats) is a more frequent source of infection. Of course, any executable file whose origin/authenticity is uncertain could be a culprit.
The email delivery should be avoidable exercising safe hex and not opening attachments or clicking links in unsolicited emails. The other means of delivery downloading game hacks/cheats, there, cracks and key-gens are a huge vector for malware infection. So avoiding those hacks, cracks and key-gens should offer limited protection.