Hackers claim to have 756 gigabytes of data taken from Grubman Shire Meiselas & Sacks, including emails and contracts.

They are demanding payment from the New York law firm, which said it is working with cybersecurity experts.

The firm said in a press statement: “We can confirm that we’ve been victimised by a cyber-attack. We have notified our clients and our staff. We have hired the world’s experts who specialise in this area, and we are working around the clock to address these matters.”

Other clients of the firm include Sir Rod Stewart, Sir Elton John, Lady Gaga, Lil Nas X, The Weekend, U2 and Drake, Sony Corp and Mike Tyson.

The hackers – known as REvil or Sodinokibi – previously attacked Travelex with ransomware.

Brett Callow, of Emsisoft, a cyber-security company, said: “Companies in this position have no good options available to them. Non-payment of the demand will result in the information being published; payment will simply get them a pinky promise from criminals that the stolen data will be deleted.

“These incidents are becoming increasingly commonplace and increasingly concerning. And incidents involving law firms are even more concerning due to the sensitivity of the data they hold.”