If you use an MS passport account (eg hotmail) change your password NOW!
It appears that at least 10,000 @hotmail @msn and @live accounts have been compromised, a list of theses accounts including passwords was posted to pastebin.com a site commonly used by developers to share code samples.
The list runs alphabetically from Ar thro Bl which suggests that there are more out their.
This was reported to Microsoft immediately in the UK and US by neowin and they are currently awaiting feedback on the situation.
Fundamentally if you have a Microsoft account (hotmail, live, msn, Zune etc) we strongly recommend you change not only your password by your security question as well.