I don't have precise information, and this is something which easily may
change, but here's something that may help:
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Thanks to the idiots at St. Bernard iPrism (a service that
prevents our corporate users from going to undesirable
sites) I now know that the update goes to
http://service.spynet.com/ASService/definitions.asmx
Found it in their blocked sites list and had to unblock it
before we could get our updates. See if your problem PC
can get there with Internet Explorer. There is a button
on the page that says GetLatestRulesetVersion. Don't know
if it works or not but worth a shot. If you can't get to
the site by name try:
http://216.32.240.26/ASService/definitions.asmx
If that works and going by name doesn't you probably have
a DNS hijacker or malware that packs the etc\hosts file
with fake addresses.
Get HijackThis.exe from
http://tomcoyote.org/hjt/hjt199//HijackThis.exe
Save it to C:\hjt (new folder) then Open it and select
Scan and Save Log. Note where you saved the log then
send it to me as an attachment. I can probably tell you
what to do to get rid of it.
Ron Kinner
Microsoft MVP 2004 & 2005
(e-mail address removed)