A detective unmasked as a police blogger is suing the Times after a journalist accessed his email to confirm his identity.
According to his lawyer Patrick Daulby, Lancashire policeman Richard Horton was exposed by the News International title as the author of the award-winning NightJack blog in 2009.
A civil claim with the High Court was lodged on Wednesday.
He is claiming aggravated and exemplary damages from Times Newspapers for breach of confidence, misuse of private information and deceit.
News International declined to comment.
The Leveson Inquiry into press standards has heard that former Times reporter Patrick Foster hacked into Mr Horton's emails in May 2009 to discover he was behind the NightJack blog.
Mr Foster told the paper's then-legal manager Alastair Brett and then-home news editor Martin Barrow what he had done.
Mr Brett told the inquiry he was furious when he learned what the young reporter had done.
He said he told him he had to find a way of establishing that Mr Horton was the author of the blog through sources in the public domain, which Mr Foster subsequently did.
Mr Horton sought an injunction preventing publication when he learned that The Times was planning to name him as the anonymous blogger.
The paper fought a High Court battle to go ahead with the story, which it won in June 2009.
Mr Brett admitted that legal documents filed by The Times as part of the case - one of which stated that Mr Foster established Mr Horton's identity using "publicly available materials, patience and simple deduction" - did not give the "full story".
Times editor James Harding apologised for the incident at Leveson, adding that he sorely regretted the intrusion into Richard Horton's email account by a journalist.
“I'm sure that Mr Horton and many other people expect better of the Times, and so do I. So on behalf of the paper, I apologise," said Harding.