As reported in The Register, the service, which allows small businesses to manage spending on mobile phones, was suspended after O2 was made aware that registered users could view other users' call records.

Bill Manager is a piece of software that lets registered users identify trends in mobile phone calls made, allowing them to identify anomalies.

While the application doesn't give direct access to billing details, it could have been possible for a computer hacker to write a script to gain access to a list of phone numbers assigned to particular firms, including the name of the person the mobile phone is assigned to.

Once O2 was made aware of the breach, the company replaced login details to the site with an apology, claiming the site had been closed for essential upgrades.