The BBC's online services, including the main website and iPlayer, were down for an hour last night, due to a "major network incident".
The outage occurred between 22:40 and 23:45 on 29 March, but the BBC said it did not return to full resilience until 04:00 today.
According to Richard Cooper, controller of Digital Distribution, BBC Future Media, the BBC's systems experienced a two-fold failure.
The first failure occurred in the aggregation of network traffic from the BBC's hosting centres to the internet, and the second occurred in the announcement of 'routes' onto the internet that enables BBC Online to be found.
"Our systems are designed to be sufficiently resilient (multiple systems, and multiple data centres) to make an outage like this extremely unlikely," said Cooper. "With both of these [systems] having failed, we really were down!"
Cooper added that the organisation would be taking "very hard look" at what it needs to do to prevent the problem from reoccurring.