An outage affected Hotmail, Microsoft's free Web e-mail service, over New Year's weekend and users' e-mails were lost.

Microsoft said that the e-mails have been restored. The company said it did not have numbers on how many people were affected or how long the outage lasted.

"All content should now be restored for customers who were impacted. We apologize for any inconvenience people may have felt while this was going on," the company said in a statement.

Microsoft also said iit is investigating the root cause to prevent it from happening again.

The company's proprietary Web services are watched closely because Microsoft wants to serve as a cloud computing platform to host other companies' Web services.

Update 3:51 p.m.:

Microsoft posted a blog update on what happened with Hotmail. The outage affected 17,355 accounts, and was caused by load balancing between Hotmail servers. It started on Dec. 30, and was fixed on the evening of Jan. 2, Microsoft said in the post.

"Customers impacted temporarily lost the contents of their mailbox through the course of mailbox load balancing between servers," Chris Jones wrote in the Windows Live blog.