Police believe the publishers of the News of the World were involved in hacking phones as recently as 2009, the Leveson Inquiry into press standards has heard.
Private detective Glenn Mulcaire's notebooks suggest that at least 28 News International employees commissioned him to illegally intercept voicemails, the hearing was told.
Records of his hacking activities also include references to "the Sun" and "Mirror", the inquiry heard.
Mulcaire was jailed along with the News of the World's former royal editor Clive Goodman in January 2007 after they admitted intercepting voicemail messages left on phones belonging to royal aides.
Detectives seized 11,000 pages of the disgraced private investigator's notes, in which he often wrote a first name or "private" in the top left-hand corner.
The 28 names which are legible in the papers correspond to News International employees, one of whom apparently made 1,453 separate requests for information from the private investigator.
Prime Minister David Cameron set up the Leveson Inquiry in July after revelations that the News of the World hacked the phone of murdered schoolgirl Milly Dowler after she went missing in 2002.
The inquiry, which formally began hearings at the Royal Courts of Justice in central London, was told Scotland Yard detectives have uncovered evidence that the practice was still going on seven years later.
Robert Jay QC, counsel to the inquiry, said: "According to the Met Police, News International's hacking operation had certainly begun by 2002, Milly Dowler being the first known victim. The police believe that it continued until at least 2009."
Lord Justice Leveson stressed that the freedom of the press was "fundamental" to the UK's democracy and way of life but said it must be exercised "with the rights of others in mind".