Sienna Miller accused her family and friends of selling stories to the media after journalists obtained intimate information about her by hacking her phone, Leveson inquiry in London heard today.
The British actress described how she felt "terrible" for even considering that those closest to her could betray her in this way.
She told the inquiry into press standards that she changed her phone number three times in three months after becoming concerned that personal details were finding their way into newspaper stories.
Having switched her number repeatedly, Miller said she was "pretty convinced" the leaks could not be the result of phone hacking and so accused her close friends and family of being the source.
The actress, whose films include Layer Cake, Alfie and Stardust, said a reporter found out about a particular "very private" piece of information which she had only told to four people, including her mother.
"I am very lucky, I have a very tight group of friends and a very supportive family, and to this date no-one has ever sold a story on me," she said. "But it was baffling how certain pieces of information kept coming out and the
first initial steps I took were to change my mobile number. And then I changed it again and again, and I ended up changing it three times in three months."
She added: "Naturally, having changed my number and being pretty convinced that it couldn't be as a result of hacking, I accused my friends and family of selling stories and they accused each other as well.
"I feel terrible that I would even consider accusing people of betraying me like that, especially being people who I know would rather die than betray me.
"But it just seemed so entirely paranoid to assume that your house is being bugged or you're being listened to somehow."
The inquiry into press standards is also hearing today from lawyer Mark Thomson, former Formula One boss Max Mosley, who won a record £60,000 in privacy damages over a News of the World story claiming he took part in a "Nazi orgy", and Harry Potter author JK Rowling.
Giving his evidence, Mr Mosley said he took the News of the World to court because he was so keen to "demonstrate they were liars", he said today. He proceeded with the High Court action despite being warned it would cost him dearly and bring his private information back into the public domain, he said.
Mr Mosley was the subject of a front-page article in the now-defunct Sunday tabloid on March 30th. 2008, alleging he took part in a "sick Nazi orgy" - something he strongly denied.
He was awarded a record £60,000 in privacy damages over the story. But he was fortunate, he told the inquiry, in having enough money and a bit of legal knowledge to bring the action.
“I thought ‘If I don’t do it, who’s going to?’,” he said. “Because the number of people they pick on with a really bad case who have got the means to fight it is infinitesimally small. “One of the terrible things is that unless you’re very fortunate and happen to have a lot of money, you simply can’t take this on, as things stand at the moment.”
The hearing began with a closed session of testimony from an unnamed man referred to as “HJK”, whose phone was allegedly hacked after he began a relationship with a well-known figure.
Members of the public and journalists were excluded from the hearing room in the Royal Courts of Justice in London during his appearance.
British prime minister David Cameron set up the Leveson inquiry in July in response to revelations that the now-defunct News of the World commissioned a private detective to hack murdered schoolgirl Milly Dowler's phone after she disappeared in 2002.
Kate McCann told the inquiry yesterday that she felt like "climbing into a hole and not coming out" when the News of the World printed her intensely personal diary in September 2008. She described feeling "totally violated" by the paper's publication of the leaked journal, which she began after her daughter Madeleine disappeared on holiday in Portugal in 2007.
The first part of the Leveson Inquiry is looking at the culture, practices and ethics of the press in general. The second part, examining the extent of unlawful activities by journalists, will not begin until detectives have completed their investigation into alleged phone hacking and corrupt payments to police and any prosecutions have been concluded.
PA