The newspaper confirmed its special investigations correspondent Amelia Hill was speaking to officers as Scotland Yard carried out its 16th arrest of the fresh investigation.
Ms Hill, who has broken a string of exclusives surrounding the investigation, was contacted by police after a 51-year-old detective was arrested by his own force last month.
A Guardian News and Media spokeswoman said: “We can confirm Amelia Hill has been questioned in connection with an investigation into alleged leaks.
“On a broader point, journalists would no doubt be concerned if the police sought to criminalise conversations between off-record sources and reporters.”
Ms Hill was questioned under caution several days ago, the paper said.
Confirmation of her contact with police came after detectives investigating illegal phone interceptions at the News of the World swooped on a 35-year-old man’s home before dawn.
He was taken to a north London police station for questioning on suspicion of conspiracy to intercept voicemail messages.
The man, who has not been named, was held by police at 5.55am today.
A series of high-profile figures have been held for questioning, including former News International chief executive Rebekah Brooks and ex-Downing Street communications chief Andy Coulson.
The scandal has already led to the closure of the News of the World after 168 years and the resignation of Metropolitan Police Commissioner Sir Paul Stephenson and Assistant Commissioner John Yates.