Hackers have attacked the website of top showbiz attorney Allen Grubman, demanding up to $7 million while threatening to reveal personal details of his clients including Elton John, Lady Gaga and Barbra Streisand.

Grubman Shire Meiselas & Sacks’ site is down, and the hackers claim to have 756 gigabytes of data including contracts and personal e-mails. A screenshot alleged to be a contract for Madonna has already been released.

Multiple sources tell Page Six that the FBI is investigating, while the NYC and Los Angeles law firm says it has notified its famous clients.

One source said, “The hackers got into the system while everyone was focused on the coronavirus. We assume, but there is no confirmation, that the hackers are Russian. They started demanding a $7 million ransom, but negotiations have taken place, taking it down to $2 million.”

The source added of Grubman — the father of famed public relations pro Lizzie Grubman — “His clients are begging him to pay the ransom to make this go away. This law firm has sensitive details on everything — work contracts, confidential settlements and endorsement deals for the biggest stars in Hollywood.”

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

Musicians represented by the firm include Barry Manilow, Rod Stewart, Lil Nas X, The Weeknd, U2 and Drake. Other clients listed are Priyanka Chopra, Robert De Niro, Sofía Vergara, LeBron James and Mike Tyson.

The hackers are reportedly known as REvil or Sodinokibi, and in January attacked foreign exchange company Travelex with malware that encrypts data until a ransom is paid in untraceable cryptocurrency bitcoin. Reps for Allen Grubman did not comment.