Mobile network operator O2 has apologised to its customers for a technical error that accidentally revealed users' mobile phone numbers to any web site they visited over 3G or WAP mobile internet connections.
Writing in a blog post the firm explained that whereas only "trusted partners" were meant to receive the phone numbers of customers that browsed certain sites, a change in its network inadvertently released this information to all web sites.
"Technical changes we implemented as part of routine maintenance had the unintended effect of making it possible in certain circumstances for web site owners to see the mobile numbers of those browsing their site," it said.
"We would like to apologise for the concern we have caused."
The firm confirmed the data had been leaked since 10 January but said it had fixed the issue as of 2pm on Wednesday after being alerted to the issue.
It explained that the firms it does usually share the information with are sites that work with O2 on issue such as age verification, content billing, for downloads, and its own services.
In light of the incident the Information Commissioner's Office (ICO) is investigating and O2 confirmed it would be cooperating with the organisation and revealed it had also reported the incident to Ofcom.
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