The leak did not give away the end of the story, or which of the main characters dies but JK Rowling and her publishers yesterday slapped a $100m (£60m) writ on the newspaper that carried it.
The author and her US publishers, Scholastic, launched a lawsuit for "punitive damages" against the New York Daily News for reproducing in legible text two pages of Harry Potter and the Order of the Phoenix.
The book, the fifth Harry Potter, is under a strict publication embargo until midnight tonight. The legal action is part of an all-out worldwide campaign to crack down on advance copies, or attempts to disclose any scrap of its contents.
In London, lawyers tabled a high court claim against the Sun for its handling of stories about the discovery of stolen copies.
The Guardian and other papers received a written solicitors' warning reiterating the ban.
In Montreal, Rowling's Canadian publisher, Raincoast, reportedly offered a woman $5,000 for immediate return of a copy sold to her by mistake by a shop.
She refused, saying: "I haven't finished reading it."
The Daily News copy came from another shop mistake. The paper carried a graphic of the two pages, as "a brief glimpse into the 870 action-packed pages", urging readers: "If you don't want to know anything about how Harry and his pals spend their fifth year at the Hogwarts School of Witchcraft and Wizardry, stop now and buy the book when it's officially released Saturday."
Yesterday, the Daily News withdrew the pages from its website. But the leaks appeared to continue. Another website yesterday afternoon was offering three different ways of downloading the book from file-sharing sources.
The public demand that triggered these disclosures was reflected by reports of Australians trekking 500km (300 miles) from Uluru (Ayers Rock) to buy the new Harry Potter in the nearest town selling it, Alice Springs.
In Johannesburg, South Africa, where new books are unaffordable for many, a bookshop reported "unheard-of orders" of 900, more than for Nelson Mandela's Long Walk to Freedom.
