I do know that the TimThumb virus specifically targets certain browser combinations - and it was known to target older IE versions because many admins do not use it (and thus it could remain undetected longer), as well as search engines (to falsely elevate the Canadian Pharmacy's search engine rankings.) I use Firefox and Chrome mostly but I do poke it with IE from time to time, as well as use the Facebook developer's debug interface to scrape the site. Posting a VFTT link on FB is what revealed the virus in the first place. None of the usual signatures of this virus have been visible since late August when I removed the last trace. I do check every few days. And, as I posted above, the load tester did find at least one spike (45 seconds), which I would expect from time to time.
I just re-ran the usual browser-side checks and get no virus signs, and 2-3 second responses, using all three browsers. I also scanned the vBulletin code on the server and it is clean.
Do please continue to report performance problems or oddities - I received some "odd" reports without specifics which weren't enough to trigger an inquiry about a virus. I now take every report of odd behavior as a possible virus.