It goes something like this. Late yesterday morning one of our Exchange servers was infected with a worm (despite being up to date on security patches and having current McAfee anti-virus .dat files). The worm apparently modified the McAfee "do not scan" list (trying to avoid detection, most likely).
Well, modding the "do not scan" list had the effect of removing the Exchange server's database files from the exclusion list. McAfee started scanning the database files as Exchange was running, and soon enough found something it didn't like. It "cleaned" the database transaction log file for our message store and *BLAMMO* Exchange had a grande mal seizure.
My crew repaired the smaller mailbox stores in the message store first, leaving the 41 GB MHIS message store for last. By 16:00 yesterday they started eseutil on our mailbox store and waited. And waited. And waited. And waited.
Microsoft's documentation suggested that, for Exchange 2003, eseutil would run roughly an hour for each 10 GB of mailbox store. We quite reasonbly through that the tool would finish by late evening. By morning it was sitting at the last stage "deleting unicode cleanup table" (WTF? That's about as informative as "PCLOADLETTER" from Office Space)
There it sat. ALL. DAY. LONG. At the twenty-two-and-a-half hour mark *BING* it was done. Exchange mounted the mailbox store, email started flowing, and life returned to normal.
The fallout will start falling on Monday. As surely as the sun will rise.