Mrs Brooks, who is also a former chief executive of the defunct paper's owners News International, was questioned for the first time at the Old Bailey, London, yesterday about what she knew of private detective Glenn Mulcaire and his hacking activities under her leadership from May 2000 to January 2003.
Asked by her lawyer, Jonathan Laidlaw, QC, if she had ever heard his name mentioned at the time, she replied: "No."
She gave the same reply when Mr Laidlaw asked if she knew of his activities, saying: "We did have private detectives working at the News Of The World."
Mrs Brooks, 45, claimed that solicitors and law firms used them more, but added: "It is common practice in Fleet Street."
Mr Laidlaw asked if phone hacking had ever been drawn to her attention. She replied: "No, not at all."
Mrs Brooks told how she became the paper's editor out of the blue in 2000, having been deputy editor of The Sun.
She had been working on an internet project with co-defendant Andy Coulson at the time and had no inkling of the promotion.
Mrs Brooks said she had been given hardly any notice of her switch in May 2000, but added that by that time she had gained experience from regularly editing The Sun.
She told the court she suggested to her boss, Les Hinton, that Mr Coulson would be a good deputy for her.
Mrs Brooks said: "We had completely different strengths and he (Mr Hinton) thought that would be a good combination.
"Andy had, I think, always been at The Sun. I had come from a features background and Andy had come more from a news background.
"Although I enjoy football, Andy is a die-hard football fan and sports fan", she said, describing how sports played a huge part in both newspapers.
Mrs Brooks said Mr Coulson had a lot of experience on a daily paper and had been showbiz editor on The Sun.
Mrs Brooks has pleaded not guilty to conspiring to hack phones, conspiring to commit misconduct in public office and conspiring to cover it up, perverting the course of justice.
She and Mr Coulson, who later became the Prime Minister David Cameron's communications director, and who is also facing similar charges, previously had an affair.
The journalist described herself as "issue-driven" and said: "The things that really affected the readers were things I got excited about."
The News Of The World's managing director Stuart Kuttner was responsible for dividing the budget into weekly spending limits for department heads, Mrs Brooks said.
She said if it was likely that a large payment would "blow" that budget, approval would have to be sought from the editor.
But she added that Mr Kuttner, who also denies conspiring to hack phones, would have to know the spending had been signed off by the editor before approving it too.
She added: "When I was made editor he said, 'You're my 17th editor, my dear' - that was how long he'd been there. Stuart, for me, had been there forever. He had an incredibly good reputation. I wouldn't say we were ever friends; he was a different generation and a different world almost. He was incredibly professional."
Mrs Brooks said that while Mr Kuttner was mainly concerned with balancing the newspaper's budget, he still had good contacts and would "dip in" to editorial matters, for example, a campaign about paedophiles following the murder of Sarah Payne in 2000.
The trial continues.
l A charge of conspiracy to pay public officials for a picture of Prince William in a bikini has been dropped against Mrs Brooks.