Hi,
Things have moved on a little and I've managed to get rid
of the problem, but I thought I'd give a summary here in
case anyone encounters something similar.
As I mentioned initially, MSAS picked up the presence of
something it referred to as Trojan Downloader BHO.Req,
identifying the file responsible as
c:/windows/system32/ddayv.dll.
After several unsuccessful attempts to let MSAS fix the
problem I disabled the BHO via IE/Tools/Manage add-ons,
and started looking on the internet for a solution.
During the next 4 hours or so the laptop was rebooted a
few times and on each occasion the BHO remained disabled.
But then, having been switched off overnight, when it was
started the following day the BHO.Req entry had
disappeared, but was replaced by another BHO identified
as MSevents Object. This time the file responsible was
identified as ddabx.dll.
I disabled MSevents and did a Google search, which
indicated that this was a symptom of the trojan Vundo. I
then followed the instructions at
http://www.webuser.co.uk/forums/showflat.php/Cat/0/Number/
216210/an/0/page/0 and successfully cleaned the laptop.
The one slight anomaly was that when I searched the hard
drive (prior to the fix) for the file ddabx.dll it drew a
blank. So where the fix instructions indicated I
should "kill" ddabx.dll on reboot, I removed the original
ddayv.dll file instead. It seems that this file has the
ability to mis-represent itself to MSAS, Hijack This and
other diagnostic aids.
So more by luck than anything else I seem to have
resolved the matter. I hope this is of some use to anyone
else who gets hit by something similar.
Bill