I found an informative blog written by a website builder... that had the older version of this Trojan on the websites she built. (-B version) http://www.zyenweb.com/2009/12/30/trojan-attack-jsillredir-b-trj/
The code she's showed on there is very similar or identical to what was on the killer abs site under the closing tag. It's important to look for things like that even if your particular AV doesn't give any alert.
As it is a trojan... it can even be that the code wasn't there when a PO accepted the page... if another web site hosted on the same server had the code, it can infect all other websites on that server!
In an ideal world ... a PO should, when a trojan like this is reported... immediately take action and stop the advertising! Then inform the hosting company ... and that hosting company should inform all other website owners hosted on the same server to check their websites and give them instructions how to remove this code if it is on their website too....
In real world ... it takes a real long time before action is taken ... giving the trojan opportunity to spread itself further and further ... Hosting companies don't have a clue ... and even if they have they are afraid to be blamed!