A 28-year-old man, understood to be former The Times reporter Patrick Foster, was arrested in London today (August 29) as part of the Operation Tuleta probe.
Scotland Yard said that he is "being questioned about alleged computer hacking relating to the identification of a previously-anonymous blogger in 2009".
It is understood that this relates to an article in The Times that year revealing the identity of police blogger NightJack.
Foster, who was also arrested on suspicion of conspiracy to pervert the course of justice, is currently being questioned at a north London police station.
He is the 11th person arrested by detectives from Operation Tuleta, which is running alongside the Operation Weeting phone hacking probe.
The Rupert Murdoch-owned paper at first denied that it had accessed emails, but later admitted that a journalist had hacked the messages for the story.
The Times was given permission to name the Lancashire detective as the author of the blog in June 2009 after the High Court denied his request for anonymity.
However, the paper's then legal manager Alastair Brett admitted to the Leveson Inquiry that legal documents filed at the time did not give the "full story".
It is alleged that Foster had been able to correctly guess security questions for the anonymous Hotmail account used for NightJack to access a range of information.
> 'The Sun' journalist arrested in computer hacking probe
At the Leveson Inquiry into press standards, The Times editor James Harding apologised and confirmed that the reporter behind the story had left the paper for an "unrelated incident".
He did not name Foster and also denied that he had given the greenlight for the email account to be hacked, but did say that he "sorely regretted" the intrusion into Horton's privacy.
He added: "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."
Horton is currently suing Times Newspapers for aggravated and exemplary damages over breach of confidence, deceit and misuse of private information.