Do you have a file on your desktop (or any other folder in your computer) that looks like the following image?

It's a bug in Outlook Express update 330994 (and 331923 before it).
If you rename that file and give it a wab extension you will discover, much to your amazement that it is a copy of your Address Book.

Due to a rather minor glitch in the update to Outlook Express it is creating the file in the wrong location and to add insult to injury it is not even giving it the proper name. The file is created whenever you edit the Address Book and then close the program you were using (Outlook Express or any other program that uses your Address Book).

There are three avenues of attack open to you.
1) Delete it. (it's really the backup copy so this may not be a good choice)
2) Ignore it (not my favorite but it might work for you)
3) R-click the file, choose "Properties" and place a check in "Hidden" then "Apply". This will only work if your system is not set to show hidden files and depends entirely on the theory that "What you don't see, won't bother you". It also has the benefit of still keeping a current backup of your Address Book on the system.

Before you ask: Yes, Microsoft is aware of the problem and they are currently trying to fit a solution into the schedule.

This bug is fixed in Windows XP Service Pack 2. After installing SP2, the backup file has the extension ".wab~" just as it should be.