Microsoft has banned a short list of countries from using its Windows Live services. Users in Cuba, Syria, Iran, Sudan and North Korea have suddenly discovered themselves coming up against "Error 810003c1".

Perusing Microsoft's support website reveals the following explanation: "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 your country".

It's unclear why just these countries are targeted, especially as the United States also has sanctions against Zimbabwe, Burma, Belarus, Côte d'Ivoire and the Democratic Republic of Congo.

As these blocks are most likely applied via IP addresses however, it would be fairly easy for residents to circumvent the blocks by using proxy servers located in countries that aren't subject to the ban.