I've just done a re-scan. No, it did not find the item again.
I had no "symptoms" - I performed the first scan because I had updated to A.V.G 2011 Free, which for the first time has a rootkit detection facility. The machine is a secondary computer which I use for limited purposes (specific websites and e-mails) and I'm pretty fastidious over not taking risks, so I was surprised when the offending file was found. I've always used F-Secure Blacklight for rootkit scans on my main computer (an XP Machine) which has never found anything save on one occasion when there was a genuine problem - which, incidentally, was successfully sorted via this forum about a year ago. I understand Blacklight to be better at ignoring false positives, but I don't think it's ever been made Windows 7 compatible.
Anyhow,the problem seems to be practically unidentifiable, so I suppose there's not a lot more to be done at this stage. Thanks for your time and help - I'll post again if anything more comes to light.
Edited by Ellinas, 31 October 2010 - 09:20 AM.