Yesterday was Patch Tuesday, and of course you have Automatic Updates set to download Critical Updates for you. Right?
But if you use Outlook 2003 you might have missed this one, which isn’t delivered via Windows Update:
Update for Outlook 2003 Junk Email Filter (KB890854)
It’s a shame that Microsoft doesn’t provide any documentation of how these filters work. They do, however, seem to be updating more frequently now. Earlier updates were irregular (December 2003, March 2004). But the most recent two have appeared on Patch Tuesday: September 14, 2004, and November 9, 2004. This update is cumulative. If you skipped the previous updates, this one gets you completely up to date.
Ed Bott 
Nice tip. I use Automatic Updates, and it did bring some in yesterday, but not this one. Thanks.