O2 has plugged a serious security hole which left its customers' account and billing details open to attack.

Users logging onto O2's (formerly Genie's) Web site are led to believe that their user name and password are sent securely using HTTPS. However, Paul Mutton (aka Jibble) yesterday created a Web page which provides evidence to the contrary.

Since O2 emphasises the need to keep passwords secure at all times its own failure to keep this information secure is a serious gaffe.

The data on Jibble's page appears genuine, but tests by security consultants Information Risk Management, show that the problem has now been fixed.

IRM's technical director Neil Barrett told us: "The story told on the Jibble page looks kosher - as though the submit commands were to a non-secure link - but we've just gone over this with a similar fine-tooth comb and it looks like it's been fixed now,"

IRM believes that the problem arose because the form input CGI was originally specified as HTTP rather than, as now, HTTPS.

O2 is investigating the issue, and wasn't able to come back with a detailed response this afternoon.

A spokeswoman for O2 said that it took security seriously and expressed surprise at the lapse. Technical staff at O2 are looking into the issue to find out what happened and when, she added. ®