Microsoft has managed to repair its Windows Azure cloud, after an expired SSL certificate downed storage and other services for people across the world.

Ninety-nine percent of the affected services have been brought back online, Redmond said early in the hours of Saturday morning, Pacific Time.

"We will continue monitoring the health of the Storage service and SSL traffic for the next 24 hours," the company wrote in a post to the Windows Azure Services Dashboard. "Customers may experience intermittent failures during this period."

The global outage lasted for around 12 hours and occurred because Microsoft failed to renew a security certificate.

The storage knockout created a cascading series of failures in other crucial parts of Azure, eventually bringing down Xbox Live components as well.

In the coming days, Microsoft will have to explain to its customers how a crucial security certificate was able to expire and bring down all secure storage services around the world simultaneously.

Some customers may be hard to mollify: a certificate problem was also to blame for a widespread eight-hour Azure outage in February of last year.

Technology industry insiders expressed a mix of disbelief and sympathy for Microsoft, with many asking how it was possible for Redmond to fall foul of such a basic error.

Netflix, a major customer of Azure's cloud rival Amazon Web Services, developed a software package around two years ago called the "Netflix Security Monkey", which automatically checked certificates on the company's cloud to avoid failures like this, its chief technology officer Adrian Cockcroft told The Register via Twitter.

The Reg's cloud desk will follow the aftermath of this story with interest, and is keen to hear Microsoft's explanation for the Blue Sky of Death. ®