A minor mistake ended up being costly for Microsoft as the company’s flagship collaboration tool Teams went offline for hours yesterday after it forgot to renew a security certificate. Teams was offline from 2PM to 5PM, with users who tried to access the service during this time met with a message that it couldn’t establish a HTTPS connection to the company’s servers.Soon after the outage began, Microsoft reached out, saying it identified the problem and was working on a fix. “We’ve determined that an authentication certificate has expired causing users to have issues using the service,” the company explained via Twitter. “We’re developing a fix to apply a new certificate to the service which will remediate impact.” Around 4:20PM the company started applying the fix, and it took around seven minutes before Teams came back online. The media were quick to criticise Microsoft for this mishap, with The Verge saying the mistake was “embarrassing”, mostly due to the fact that it recently started playing TV ads for the tool. “It’s also surprising to see Microsoft forget to renew a key certificate for Teams, especially when the company develops software like System Centre Operations Manager to monitor for things like certificate expiration.” Tech Crunch drew everyone’s attention to the fact that Microsoft failed to apologise for the outage, despite Teams being used by 20 million people.