A former News of the World investigative journalist today told an inquiry into press standards that his work had led to more than 260 "successful criminal prosecutions".
Mazher Mahmood, who was the defunct newspaper's investigations editor, told the Leveson Inquiry that his most high-profile inquiry had been into Pakistani cricketers who were subsequently convicted of match-fixing.
Mr Mahmood, who became known for disguising himself as a "fake sheikh" in order to carry out undercover reporting, said he had exposed "criminal and moral wrongdoing" during a 20-year career at the News of the World.
He gave evidence in a room occupied only by lawyers to protect his identity. His words were broadcast to an annex where journalists and members of the public could listen.
Inquiry chairman Lord Justice Leveson, who is sitting at the Royal Court of Justice in London, said he had made an order allowing Mr Mahmood, who now works for The Sunday Times, to give evidence away from the public gaze for "good reason".
Mr Mahmood was asked to describe how the checks on his stories at The Sunday Times, where he now works, compare to those at the News of the World.
He said: "It was a lot more informal at the News of the World newspaper but in essence we still had to satisfy the same criteria. But it was a lot less formal - chats with the news desk - there were no meetings."
He added that the process at The Sunday Times is "a lot more stringent", but said that at the News of the World he was in "constant touch" with lawyers.
"Everything was discussed with the legal team," he said. "I couldn't go off-piste and do what I wanted. I had to take legal advice and throughout the investigation I remained in constant touch with our lawyers."
Mr Mahmood said that the two main questions to be answered when deciding if a story about a person should be investigated was: "Are they involved in criminality? Are they involved in moral wrongdoing?"
When Lord Leveson asked Mr Mahmood if he believed that if there was a conflict between what he perceived as a famous person's public persona and the story, then it was worth investigating.
He replied: "If it's hypocrisy then very much. If they present themselves as wholesome characters and trade on that status then I think it's totally justified."
Mr Mahmood said the News of the World had been keen to adhere to the Press Complaints Commission (PCC) code of conduct.
"We were always being criticised so we were extremely cautious to comply with the PCC code," he told the inquiry.
He went on to say that he had been taken off live investigations to respond to PCC complaints.
"In 20 years I didn't have a single PCC complaint upheld against me," he said.
Mr Mahmood added: "It was quite a laborious task answering those complaints." He said that this demonstrated "how seriously we took the PCC code".
He went on to deny evidence given to the inquiry by Paul McMullan, employed by the now-defunct Sunday tabloid for seven years, that he had worked alongside him.
"This came as news to me," he said. "I may have seen him in the office. I've never worked with the chap. I can't even recall talking to him. (It is) completely untrue."
Mr Mahmood also said that media reports that he had commissioned a private detective for his investigations were "simply not true".
He added that it was a "common misconception" that he engaged in entrapment.
Mr Mahmood also justified investigations against model Sophie Anderton and a woman known as Miss X.
"The primary focus of both those stories was illegality. They were dealing drugs to clients," he said.
Mr Mahmood said the majority of his stories came from informants who had provided information in the past.
"We would make every possible check where we could before embarking on any investigation," he said. "A lot of investigations are expensive. They involve quite an investment, so we have to be sure of ourselves."
He said he was not aware of phone hacking until the arrest of former News of the World royal editor Clive Goodman, who was jailed four years ago after admitting intercepting phone messages.
Mr Mahmood said there was "of course" talk in the office following the arrest and added: "All the fingers were pointing at the newsdesk."
Mr Mahmood said he did not "entrap" people.
"It is annoying, this myth of entrapment," he said. "We don't entrap people. Frankly, I don't believe you can entrap people in the manner they suggest."
Asked about the subject of one investigation, he said the newspaper provided the "environment for him to commit the crime - a crime which he was pre-disposed to commit".
"These are people who are predisposed to commit these crimes anyway," he said. "All I am doing is providing a snapshot of what they are doing anyway.
"No matter what the size of the carrot, you cannot entrap people into committing these crimes. However, the public perception is that because they have been offered a huge carrot, that has resulted in the crime taking place."
Mr Mahmood said "exposing criminality" gave him "great satisfaction".
"I am proud to have jailed paedophiles, arms dealers and drugs dealers and the like," he said. "That is my motivation."
He said he would "cross the line" in the public interest.
"The public interest is the overriding factor. I have purchased child pornography, for example, which clearly is illegal, and that led to a conviction," he said.
"There are times when we cross the line - but the overriding factor is the public interest."
He added: "I am perfectly happy with all the 500 investigations that I have done. All 500 of them fulfil the criteria, in my view, that they satisfy the public interest."