If you're on O2's UK mobile network (not ADSL), you'll (probably) see a line beginning with x-up-calling-line-id - followed by your mobile phone number in plain text. Other operators may use different headers, or hopefully none at all - let me know - I'm interested to know if other networks are doing it too.

“@O2: @stevelacey Hi Steve, it's our top most priority, we're investigating this at the moment..." O2 seems to be taking this seriosuly

The privacy breach means that site owners could be collecting the phone numbers of visitors which could then be used for telephone and SMS marketing without the phone owner's consent. That in turn could open up phone users to reverse-charge SMS spams, which could cost them huge amounts in bills if their number is used for scams.

The Information Commissioner's Office said it is considering whether to investigate further, although a spokesman said there was no immediate breach of the Data Protection Act. A mobile phone number on its own is not classed as "personally identifying information" (PII), because it does not identify an individual on its own; but the spokesman said the office would consider whether other personal data was being processed at the same time.

I'm on O2 and I don't get the header line with my phone number appearing on that page. Maybe they have sorted this out.

im on 02 how do I check the header line?

Here’s their page about the issue.

http://blog.o2.co.uk/home/2012/01/o2-mo ... wsing.html

I am outraged! I've not read this but I'm still outraged! I'm going to write an angry letter using my green crayon.

I'm on O2 and I don't get the header line with my phone number appearing on that page. Maybe they have sorted this out.