drugrep,
The usual automatic update pattern is that the Defender definition updates
are automatically pushed out weekly or bi-weekly through AU[WU/MU] and
that's what's reported to you using the internal update mechanism, however
the actual updates are more frequent from the Ms anti-malware staff as
announced on the Calendar of Updates as manual updates:
http://www.dozleng.com/updates/index.php?act=calendar
These are available for manual download and only manual download apart from
Defender's own automated or internal update process, for example by
visiting the Malware Protection Center/ Security Portal:
http://www.microsoft.com/security/portal/
Another industry example of this is Norton's automated signature
distributions weekly, although their more current signatures are available
anytime manually by visiting Symantec's site (I've needed that exactly
twice myself.) There is nothing that prevents or forces anyone to use a
Defender manual update, it's your decision, but I think the prime intent
was to allow for special needs in the event of a serious Malware event like
a zero-day type infection, or by the logic given by Donna Buenaventura:
"Useful for users who are:
1. Stucked for old defs for some reasons e.g. problem with MU, WU in
downloading and installing the updates.
2. Want to deploy the signature update offline
3. Want to take advantage of the this cool service by MS to have new defs
everyday.
Dial-up users might not like though for it is more than 3megs download.
They should wait for weekly updates instead that is pushed thru MU."
