A massive data outage for Sidekick handheld users has become a massive PR headache for Microsoft and carrier T-Mobile.

A massive data outage in Microsoft's Danger unit left many T-Mobile Sidekick users without access to their calendar, address book, and other key data. However, things got even worse as Microsoft said in a statement that data not recovered thus far may be permanently lost. Microsoft and T-Mobile have not said how many of the roughly 800,000 Sidekick customers have lost data.

Week in review: Data loss disasters