An undisclosed technical glitch blocked users from logging on to Microsoft Corp.'s free Web-based e-mail service and other sites Tuesday.
(Msnbc.com is a joint venture of Microsoft and NBC Universal.)
After several hours, the software maker was able to reduce but not completely fix the problem that left Web surfers around the world unable to access Hotmail and other services that require a Microsoft login. Those include the Xbox Live video game community site and the Windows Live Messenger instant messaging program.
"The issue is purely impacting the login process for customers and largely does not impact customers who were already logged in," said Microsoft spokeswoman Samantha McManus in a statement. "We have made significant progress in decreasing the number of customers currently affected since initial reports, but the issue has not yet been completely resolved."
Microsoft did not say what caused the problem.
McManus said the sites will be working again for all users "shortly."