An Internet routing error by AT&T effectively shut off access from around 40% of the Internet to several major Microsoft Web sites and services on Thursday, Microsoft has said.Access to Microsoft's Hotmail, Messenger and Passport services as well as some other MSN services was cut for more than an hour after AT&T made routing changes on its backbone. The changes were made in preparation for the addition of capacity between AT&T and Microsoft that is meant to improve access to the services hit by the outage, Microsoft spokesman Adam Sohn said."We are doing some work with AT&T to add more capacity and better route traffic between AT&T's network and Microsoft's services," he said. "AT&T made some changes in preparation for this and the effect was that traffic was incorrectly directed causing some of our services to become unavailable to 40% of Internet users at peak.""Microsoft services were up and running but people could not get to them," he said.Thursday's outage ran from 1:15 p.m. PST to 2:30 p.m. PST (21:15 to 22:30 GMT) although problems might have lingered for some users, Sohn said.The problem is unrelated to an outage on Monday this week that left most of MSN Messenger's 75 million users unable to access the service for around five hours, said Sohn. "We had not started the work with AT&T on Monday."