BT suspended the services available from its Web site for two hours today after an upgrade to its site went horribly wrong.
An upgrade to BT's site, which sources suggest involved improving security measures for access to customer phone bills online, had exactly the opposite effect.
A number of Register readers have written to say that when they logged on to access their own bills they were able to see other people's bills online.
Mike Bartlett, a press officer at BT, confirmed that services were suspended after customers notified the telco about security problems, which he said had now been resolved. BT brought Web-based services back online at 15:45 UK time today after suspending them at 14:00.
A programming error meant that customer's logging onto BT's 'View My Bill' service would see the bill of the last person to use the service and not their own, he said.
Bartlett said BT would review its procedures in light of today's problems.
BT said the programming error did not mean that it was possible to search its database for customer's phone records - an assurance that has been questioned by security experts.
Paul Rogers, a network security analyst at MIS Corporate Defence, said that anyone who registered onto BT's site to use the bill viewing feature could see other people's phone bills if they knew the customer reference number associated with a phone number.
"You don't need to register to view details," said Rogers. "The system hasn't been changed to include proper authentication and BT are still assuming trust."
Rogers said the problem was similar to an outstanding security issue with BT Cellnet's Web site, which made it possible to impersonate someone by intercepting or stealing a user's session ID.
BT needs to carry out a thorough security review and audit, he added. ®