Microsoft Lync, June 23

The instant messaging and VoIP service, part of the Office 365 suite of cloud-based business products, went down on June 23 in much of North America before noon EST.

For some users, the outage, which Microsoft said was caused by "external network failures," lasted up to eight hours.

Microsoft said connectivity was restored in minutes, but an ensuing traffic spike overloaded their network and extended the outage. Customers complained Microsoft was not keeping them apprised of what was happening.