A law firm used by A-list celebrities including Madonna, Elton John and Lady Gaga has been hacked by cyber attackers.
The website for Grubman Shire Meiselas & Sacks has crashed and hackers claim to have 756 gigabytes of data including contracts and personal emails.
The cybercriminals have released an image purporting to show a Madonna contract and have demanded payment, the BBC reported.
“We can confirm that we’ve been victimised by a cyber attack,” Grubman said in a statement.
“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.”
It is not clear how much money the hackers have demanded and whether Grubman is negotiating with them.
The New York law firm specialises in music and entertainment, and counts top stars such Rod Stewart, Barbra Streisand and Robert de Niro among its clients.
Drake, Barry Manilow, The Weeknd, Madonna, Andrew Lloyd Webber and Priyanka Chopra are also all thought to use the firm.
The attack was carried out by a group known as REvil, which previously carried out a devastating ransomware campaign against foreign exchange giant Travelex.
Read more: Travelex held to ransom by hackers
“This breach appears to be a surgical strike against Grubman, knowing they represent many of the biggest celebrities in the world,” said Sam Curry, chief security officer at cybersecurity firm Cybereason.
“Unfortunately, there are no longer any guarantees for companies that decide to pay a ransom because there is less and less honesty amongst these cyber criminals. Paying a ransom no longer guarantees a return of proprietary information.”