Internet service providers America Online, Virgin.net, Wanadoo and Zen Internet all confirmed that they had been hit by outages. BT, U.K.'s telecommunications giant, said the glitches, which affected people between 8:30 a.m. and 11:30 a.m. PT, were due to a software problem linked to user authentication.
Three servers were the cause of the problem, which affected customers randomly around the United Kingdom, according to BT.
A BT representative said the outages resulted from increased congestion on the network, preventing fresh users from logging on, although those already connected via BT's broadband network experienced no service interruption.
Although none of the ISPs could immediately provide precise information on how many end users experienced problems, a Zen representative described the outages as "short term but significant," and a representative for Wanadoo said most ISPs had been touched by the problems at BT.
AOL estimated that the number of its subscribers who experienced Internet connectivity problems could have reached 100,000. "It's a pretty busy time of the day," an AOL representative said.
BT's representative said the company has launched an investigation into the problem.
Jo Best of Silicon.com reported from London.