The newspaper has followed the phone hacking scandal since the outset, with journalist Nick Davies breaking the story, including the revelation that murdered schoolgirl Milly Dowler had her voicemails intercepted by journalists at the News of the World.
Deputy Assistant Commissioner Sue Akers, who is in charge of Operation Weeting, said: "I made very clear when I took on this investigation the need for operational and information security. It is hugely disappointing that this may not have been adhered to.
"The MPS (Metropolitan Police Service) takes the unauthorised disclosure of information extremely seriously and has acted swiftly in making these arrests."
The detective is reported to be a 51-year-old man who was working on the phone hacking investigation. He was said to be arrested at his desk and later suspended from his position.
Earlier this week, Conservative MP Louise Mensch said on Twitter that it was wrong for documents in the investigation - such as Clive Goodman's letter to News International - to be leaked to The Guardian before their official publication.
"It is pretty shoddy stuff that somebody leaked documents to the Guardian before they were published. Nobody should be handing out exclusives," she said.
In response to the latest developments, Mensch - who is a member of the Culture, Media and Sport Committee - added: "You know, I do feel completely vindicated that EVERYBODY in Fleet Street was hacking, blagging or colluding w/police. EVERYBODY.
"If it was yesterday's docs it was illegal. We say nowt (sic) til they are published. Not for one paper to get exclusives."