The 45-year-old told the Old Bailey in London that she had never been asked to sanction the use of phone hacking to get stories while she was editor between 2000 and 2003.
But she admitted she did not actually know the practice was illegal, saying: “If you took my editorship of the NotW at the time, I don’t think anybody, me included, knew it was illegal.
“No-one, no desk head, no journalist, ever came to me and said ‘We’re working on so-and-so a story but we need to access their voicemail’ or asked my sanction to do it. It just didn’t happen in the course of my editorship.”
She said even though she did not know it was illegal, she would still have felt it was a “serious breach of privacy.”
But she said although she had never sanctioned hacking, she might have done in the right circumstance and if there was a strong public interest.
She said: “If somebody had come to me with the right set of circumstances and asked me … something to do with paedophiles, Roy Whiting … something along those lines … and had asked me with a good set of reasons, I may have done.”
Brooks, of Churchill, Oxfordshire, denies conspiring to hack phones, to commit misconduct in public office, and to cover up evidence to pervert the course of justice.
In the witness box for the third day yesterday, the former News International chief executive was questioned about the 2002 story of murdered Surrey schoolgirl Milly Dowler, which was to go on to bring about the Sunday tabloid’s downfall.
Milly disappeared on 21 March 2002, the court heard, and, while still missing, her voicemails were hacked the following month, between 10 and 12 April. Asked about her reaction when she found out in 2011 that Milly’s phone had been hacked by the NotW when she was at the helm, Brooks said: “Shock, horror, everything.
“I was told that the NotW had asked someone to access Milly Dowler’s phone while she was missing, that they had also deleted her voicemails and, for a period of time because of that, her parents had been given false hope and thought she was alive.
“I just think anyone would think that that was pretty abhorrent, so my reaction was that. That was what I was told.”
The court heard that Brooks was on holiday in Dubai with then-partner Ross Kemp from 7 to 14 April, leaving her then-deputy Andy Coulson, a co-defendant in the trial, in charge.
Under questioning from her lawyer Jonathan Laidlaw QC, Brooks said the fact that private investigator Glenn Mulcaire – who pleaded guilty to phone hacking – had been tasked with hacking Milly’s phone was never brought to her attention before 4 July 2011.
She said she did not remember any discussion about Milly’s disappearance when she checked in with her staff, and did not recall leaving a conversation in Dubai to take a phone call about the missing schoolgirl.
Brooks said the high level of contact while she was away between her and the NotW – including calls to the editor’s office and texts with Coulson – was not “at all unusual”, as she checked on the progress of that week’s edition.
But she denied playing any part in the apparent removal from the paper of the text of a hacked voicemail message mistakenly left on Milly’s phone by a recruitment agency, which appeared in the NotW’s first and second edition on 14 April, but later disappeared from the third, as well as a decision to move the article from page nine to page 30.
Asked by Mr Laidlaw what she would have done if someone had told her on the Thursday or Friday that they had a lead on the whereabouts of Milly, Brooks said she would have told them: “Tell the police.
“If they had not, I would have told them to do so.”
Earlier, Brooks said she was unaware of a £92,000-a-year contract the paper had with Mulcaire and said although the use of private detectives by Fleet Street at the time was “pretty normal”, she had never heard of his name before he was arrested.
The case continues.