London (CNN) -- Paparazzi hounded "Harry Potter" author J.K. Rowling so constantly after her children were born that she felt like a hostage in her own house, she told a government-backed inquiry into British press ethics and practices Thursday.
She could not go outside without being photographed for a week after the births of her second and third children, she told the Leveson Inquiry.
And it was "hard to say how I angry I was" at finding that a journalist had managed to slip a note into her 5-year-old daughter's school bag, she said.
"A child, no matter who their parents are, deserves privacy. ... It's a fairly black-and-white issue," she said, arguing that a child had no say in who their parents were or what they did.
She had to move out of an earlier house because of harassment by journalists, she said.
"I really was a sitting duck for anyone that wanted to find me," Rowling said of the home she bought just as her fictional boy wizard became a worldwide sensation in 1997.
Rowling then described how a manuscript of one of her books was stolen from the printers and came into the hands of The Sun newspaper after apparently being found by an unemployed man "in a field."
She had to take legal action to prevent the contents of the book being revealed pre-publication, she said, and felt The Sun was trying to turn the situation into a photo opportunity.
"I felt I was being blackmailed -- what they really wanted was a photo of me gratefully receiving back the stolen manuscript," she said.
Rowling said a "wholly untrue" Daily Express story, which claimed she had based an unpleasant character on her ex-husband, had meant she had to have a "horrible" conversation with their young daughter to explain that it was not the case.
"This episode caused real emotional hurt," she said, because her daughter had to cope with other children believing that about her father.
Rowling added: "It portrayed me as a vindictive person who would use a book to vilify anyone against whom I had a grudge."
Rowling also pointed to a story published in the Sunday Mirror, which claimed her husband had given up his job as a doctor "to be at the beck and call of his obscenely rich wife," she said.
This was "damaging misinformation" about her husband, who is not a celebrity, she said, because it led colleagues to believe he had abandoned his medical career. The paper subsequently apologized.
Defamatory articles spread like fire and are difficult to contain, she told the inquiry, but she had no "magical answer" to the problem of abuses by the press.
Actress Sienna Miller told the probe earlier Thursday it was "terrifying" to be hounded by press photographers as a young woman.
She described being a 21-year-old chased in the dark by packs of men, and she said press hounding had made her "intensely scared" and "paranoid."
"Every area of my life was under constant surveillance," the "G.I. Joe" actress said.
Miller got a £100,000 ($155,000) payout this year from the publisher of Rupert Murdoch's News of the World newspaper over phone hacking.
But she told the inquiry she had sued for information about who was hacking her, not for the money.
The parliamentary probe in which she testified was set up in response to outrage at revelations of the scale of illegal eavesdropping and police bribery on behalf of News of the World, which Murdoch's son James shut down in July over the scandal.
Police are investigating phone hacking and bribery in separate investigations, and Thursday announced their first arrest in a related probe.
London's Metropolitan Police arrested a 52-year-old man on suspicion of computer hacking early Thursday in Milton Keynes, outside of London, they told CNN.
Also on Thursday, the Leveson Inquiry announced that it would call former British newspaper editor Piers Morgan as a witness.
Morgan, who now hosts an interview program for CNN, "Piers Morgan Tonight," said he would appear.
Former Formula 1 motor racing boss Max Mosley took the stand at the Leveson Inquiry after Miller.
Mosley sued the News of the World after it ran a front-page article claiming he had organized a Nazi-themed orgy with multiple prostitutes. A court found in his favor, saying there was no Nazi element to the event.
Mosley said the source of the story was one of the women involved, who wore a hidden camera and was coached by a News of the World reporter to try to get Mosley to make a Nazi salute.
The Leveson Inquiry has been hearing from high-profile figures all week.
The mother of missing British girl Madeleine McCann told the inquiry Wednesday that she felt "totally violated" when she saw her diary had been published in the News of the World newspaper.
"I'd written these words at a most desperate time of my life," Kate McCann said, adding that the newspaper had shown "no respect ... for me as a mother or human."
The publication of Kate McCann's diary came after the editor of the now-defunct newspaper, Colin Myler, verbally beat her and her husband, Gerry, "into submission" to make them do an interview with the newspaper, Gerry McCann said.
Tabloid newspapers published articles suggesting the parents were responsible for their daughter's death, Gerry McCann said, forcing them to sue to demand retractions.
"We could only assume they were acting for profit," he said of the newspapers, adding the articles had no basis in fact.
Madeleine McCann and her parents have been regular fodder for Britain's tabloid press since the 4-year-old disappeared more than four years ago from a resort in Portugal while her parents dined at a nearby restaurant.
The girl has never been found.
Most of the inquiry's attention has focused on newspapers owned by Rupert Murdoch's News Corp., but the McCanns described their troubles with other newspapers, including the Daily Mail and the Evening Standard, which are not News Corp. titles.
News Corp. announced Wednesday that James Murdoch had stepped down in September from the boards of subsidiaries that publish The Sun, The Times and The Sunday Times.
He remains chairman of News International, the News Corp. subsidiary that owns all three newspapers.
Police investigating phone hacking by journalists say that about 5,800 people, including celebrities, crime victims, politicians and members of the royal family, were targets of the practice by journalists in search of stories.
It involves illegally eavesdropping on voice mail by entering a PIN to access messages remotely.
CNN's Laura Smith-Spark, Atika Shubert and Per Nyberg contributed to this report.