The Microsoft Teams service abruptly stopped working for about three hours after Microsoft forgot to renew a security certificate.
The users of the Microsoft service that competes with the application Slack encountered error messages when trying to log in to the service Monday morning. Microsoft informed them that it was unable to establish an HTTPS connection on the company's servers.
Microsoft confirmed that the Teams service was down on Monday, then revealed what it was problem.
“We found that a cert control identity has expired causing problems for users of the service," Microsoft says.
Then the company began to applies a fix and the service has been restored for most users.
It was a very annoying mistake by the company and of course it is surprising that a company the size of Microsoft forgot to renew a key certificate of a service, especially when developing software like System Center Operations Manager tracking things like certificates expiring.