Two South African brothers have allegedly vanished with bitcoin worth $3.6 billion in client funds after claiming their trading system was hacked.

Johannesburg-based news website Independent Online (IOL) said the brothers, owners of crypto currency investment company AfriCrypt, allegedly disappeared with 69,000 bitcoins and are believed to have fled to the United Kingdom. They allegedly told about 20 investors in their company not to tell the police as that would slow the recovery process.

“We regret to inform you that due to the recent breach in our system, client accounts, client wallets and nodes were all compromised,” AfriCrypt said in a statement, according to IOL.

“Unfortunately, this has forced Africrypt to halt operations… We urge all clients to please be patient as we attempt to resolve the situation. It is understandable that clients may proceed the legal route, but we ask clients to please acknowledge that this will only delay the recovery process.”

A lawyer for the victims told IOL that the funds were “subjected to various dark web tumblers and mixers, resulting in severe fragmentation“, making them virtually untraceable.