O2 and Tesco Mobile send your phone number to every site you visit using their mobile data network

Lewis Peckover, who set up a little web tool that displays all the “HTTP header information” sent to sites by web browsers, highlighted yesterday that O2 include your mobile phone number whenever you visit a website whilst running over the 3G network.

Users of the social news site, Reddit.com, confirm this problem also happens with Tesco Mobile.

For O2 and Tesco customers browsing on a 3G connection, these headers also include their personal telephone number in an x-up-calling-line-id line. Enterprising website owners can easily keep a copy of the HTTP header information sent over by visiting browsers and tie it to IP addresses and logins, if applicable.

O2 commented on their Twitter feed:

@lewispeckover Hi Lewis. The mobile number in the HTML is linked to how the site determines that your browsing from a mobile device #O2Guru  (https://twitter.com/#!/O2/status/161872584634408960)

But, this is bollocks.  Browsers send a User-Agent line in the Headers that tells web servers what browser and operating system it’s using, rather than having to divulge personal details such as the users mobile telephone number.Customers on an O2 or Tesco Mobile monthly contract might want to talk to a lawyer in regards to the validity of the contract now that it has been seen O2 are willy-nilly giving out these personal details to all websites you visit.