Steam went down shortly before after 11:30 a.m. ET today, and according to Valve, the company's regular morning maintenance is to blame.
"The routine maintenance on Steam servers this morning, Tuesday Sept 25th, 2012 is taking longer than expected," said Valve on its Facebook page. "We appreciate your patience."
As seen on Steam's user activity chart above, the concurrent users on the service dropped from nearly 4.3 million to zero between 11:30 a.m. and noon. We'll update this article as soon as we have more information from Valve.
Update: Steam is functional once again. According to Valve, the planned Steam downtime ''ran a lot longer than we had anticipated." The company added, "We apologize for the inconvenience."