Glitch means mobiles may reveal details
So what are the risks?
The risksThe Guardian has warned that many of the UK's 2.2 million O2 users could be inadvertently revealing their telephone numbers when they browse the web.
A certain amount of information is always sent when you browse using your phone. It is forwarded automatically to the website owner, so they are able to format the site to suit your handset. There is always some additional information packaged with this data, but in this instance it appears that the mobile phone number has been included.
The risk is that once websites have these numbers, they could be used to market direct to people's phones, either by cold-calling or texting. This in itself doesn't break any laws, although clearly users would be outraged to find they were being left vulnerable like this. And if users are browsing sites with a less ethical approach to doing business, there is no knowing how they might choose to use the information.
Check your phoneThe newspaper reported that the data breach was identified by a London programmer, who was looking into how to identify whether a website's users were logging on through their mobile phones. He alerted the newspaper, which has now contacted the mobile phone company. O2 is said to be investigating what is happening and why the number is being forwarded.
So what can you do?
The good news is that people on other networks don't seem to be affected by the glitch. Blackberry users on O2 are safe too, possibly because of the system the handset uses to connect to websites - which differs from other types of phones.
If you want to check if your number is being forwarded the programmer who discovered the error has set up a website to enable you to detect whether your number is forwarded, so you can test your phone here.