Outlook Express ~.dat file showing up

My friend is running Windows ME (yeah I know) and she keeps having a file called ~.dat showing up on here desktop. I opened the file in notepad and noticed a bunch of email address prefixed with STMP, so I imported it into excel, and minus a few non-ascii characters each row was an email address. I changed the extension to .wab and was able to import it perfectly in to Outlook Express as a Address Book.

She is not requesting this file be created and doesn't know why it is showing up. I will be able to access her PC sometime this week and will update any new information I can get.