There has been an outage affecting customers of Windows Live Messenger and Hotmail. It lasted about one hour; people could not sign in using Windows Live ID during this time. The Windows Live ID team has kept people up-to-date via their Twitter account and published an explaining post afterwards on the Inside Windows Live Blog. Arthur de Haan, responsible for test and system engineering at Windows Live, says:
Due to the failure of one server, Windows Live ID logins were failing for some customers, and this increased the load on our remaining servers. […] We identified the root cause and fixed it in less than an hour, but it took a while to resolve the logjam that had built up in the meantime, and to redistribute the load to normal levels.