Users in Cuba, Syria, Iran, Sudan and North Korea can no longer IM with Windows Live Messenger.

When trying to log in they will be left with error message:
810003c1: We were unable to sign you in to the .NET Messenger Service.

Reason: Microsoft has shut off the Windows Live Messenger IM for users in the countries embargoed by the US, hence Microsoft no longer offers Windows Live Service in those countries.

Source: Messenger Support Space - Error 810003c1

Edit: Looks like the Messenger Support space prefers to delete posts and write new instead of editing... The source article can now be found here.

The country names have been taken out and the reasoning has been reworded to:
“Microsoft has discontinued providing Instant Messenger services in certain countries subject to United States sanctions. Details of these sanctions are available from the United States Office of Foreign Assets Control.”

To be honest we don’t understand why an embargo would lead to this (and why now?), it’s not like offering a free service (Worldwide) is doing business…or is it? And why not list the countries anymore…