O2 has apologised for exposing customer mobile phone numbers to website owners, fixing the issue amidst hefty criticism.
The company was caught out by Lewis Peckover, a system administrator for a mobile gaming company, who revealed what O2 was doing via a specially-crafted webpage showing information the site received about visitors.
When an O2 phone connected to the site it showed the telephone number in plain text. No other operators were guilty of doing the same.
O2 has now stopped sharing customer numbers in this way, but many remain concerned about what companies have their contact details.
O2 issued an FAQ on its official blog, claiming it only shared numbers with "certain trusted partners," but a mistake made during technical changes meant website owners could see them.
Numbers started being shown to website owners from 10 January.
"We share mobile numbers with selected trusted partners for 3 reasons: 1) to manage age verification, which manages access to adult content, 2) to enable third party content partners to bill for premium content such as downloads or ring tones that the customer has purchased 3) to identify customers using O2 services, such as My O2 and Priority Moments," the company said.
"This only happens over 3G and WAP data services, not Wi-Fi."
Despite its explanation of why it was sharing users' telephone numbers, O2 still decided to fix the issue.
It has also contacted the Information Commissioner's Office (ICO), saying it would be cooperating fully. Ofcom has also been informed.
