Police did not identify the suspect, but he was believed to be Jamie Pyatt, 48, who has been with the paper for 24 years and is now the district editor, The Guardian reported. He was brought in for questioning about alleged illegal payments to police officers.
The Sun is owned by News International. The company, part of Rupert Murdoch's global media empire, this summer shut down The News of the World in an attempt to deflate the hacking scandal.
Friday's arrest was the sixth in Operation Elveden, the investigation into alleged police payoffs.
Police said this week nearly 2,000 more people may have been victims of phone hacking than previously thought.
London's Metropolitan police, who told a Parliament hearing earlier this year that investigators identified 3,870 names, said Thursday they found 5,795 names in notes seized from Glenn Mulcaire, the News of the World investigator jailed in 2007 for phone hacking, The Daily Telegraph reported.
"It is not possible to give a precise figure about the number of people whose phones have actually been hacked but we can confirm that as of [Thursday], the current number of potentially identifiable persons who appear in the material, and who may therefore be victims, where names are noted, is 5,795," Scotland Yard said in a statement. "This figure is very likely to be revised in the future as a result of further analysis."
Police stressed that being named in Mulcaire's notes didn't mean a person's telephone was hacked.
Scotland Yard has been roundly criticized for its estimates of the number of phone-hacking victims, originally estimated to be only a "handful."
Most of the known victims have been celebrities, including members of the royal family, and victims of notorious crimes like the London Transport bombings. The scandal exploded this year when The Guardian reported the News of the World hacked the cell phone of missing schoolgirl Millie Dowler before her body was found in 2002.
Also Thursday, the judge overseeing the case, granted requests by singer Charlotte Church and television personality Jacqui Hames to be included in the inquiry into media ethics and phone hacking, the Telegraph reported.
The judge rejected an application by Surrey Police, who recently admitted they knew slain schoolgirl Milly Dowler's phone was hacked in 2002 but did not investigate. The police force's attorney said phones of investigating detectives also were hacked.
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