The company said that a coincidental failure of two parallel data center system left people without the micro-blogging service.
Twitter blamed an "infrastructural double-whammy" of two data center failures on the outage that left millions without the micro-blogging service for hours today.
Twitter's site went down between 8:20 a.m. and 9 a.m. PT and was out for about two hours before the company had the service back up and running.
Typically, if one data center goes down, there's another one in place for emergencies and redundancy. But the company said in a blog posting that the parallel systems went down at nearly the same time.
"I wish I could say that today's outage could be explained by the Olympics or even a cascading bug," the company said in its post. "Instead, it was due to this infrastructural double-whammy. We are investing aggressively in our systems to avoid this situation in the future."
As a younger company, Twitter suffered from frequent outages caused by its explosive growth. Over the last couple of years, however, most of those outages have subsided, save for a few brief outages from time to time.
Twitter suffered an outage last month that left its site unresponsive for about an hour. The company said that the issue was caused by a "cascaded bug in one of our infrastructure components," but provided no further details.
The outage followed a similar hiccup with Google's chat service, Google Talk, which was briefly down earlier this morning.