Cyberattackers who broke into celebrity law firm Grubman, Shire, Meiselas and Sacks have threatened to lay open business deal of their A-list clients including Bruce Springsteen's Netflix deal and Sean "Diddy" Combs' rumoured $100 million vodka deal. The law firm has refused to pay up the hacker group a ransom of $42 million.

Celebrity attorney Allen Grubman's New York law firm represents stars including Lady Gaga, Madonna, Mariah Carey, U2, Bruce Springsteen. Besides, Priyanka Chopra and Bette Midler also figure in the client list. The law firm was shaken by hackers group REvil, who attacked them for $21 million, on Wednesday. REvil is being probed by the US Secret Service and the FBI. The hackers stole 756 gigabytes of confidential documents relating to Grubman's firm's clients.

On Thursday the hackers upped the ante by demanding a sum of $42 million as ransom. They also threatened to publish "a ton of dirty laundry" on US President Donald Trump next week if the amount is not paid. However, Trump is not a client of the law firm.

"Grubman isn't going to pay these cyber-terrorists a penny, so it is likely all his files will end up released by the hackers. The interesting details in there could include U2's lucrative publishing deals with Universal, worth an estimated $300 million, as well as Springsteen's deal with Netflix, estimated to be worth $20 million, as well as how much Diddy actually made in that Ciroc vodka deal," a source told Page Six who has knowledge of the hack.

"Often, the most damaging details are in the personal emails of the stars and the executives — which is what happened with the 2014 Sony hack. But it is not known how many personal emails have been stolen from the Grubman hackers," the insider added.

Hip-hop mogul Sean "Diddy" Combs
Hip-hop mogul Sean "Diddy" Combs hit out at the Grammys for failing to "respect" black music -- even as he was honored as an industry "icon". Photo: AFP / Mark RALSTON

On Thursday REvil posted documents relating to Lady Gaga on their web site, that appeared nothing more than standard industry contracts.