The world’s largest bitcoin exchange OKCoin has suspended some of its services indefinitely, following a malicious cyber attack from unknown hackers.

Due to an increasing number of complaints on bitcoin forums and panels including and Bitcoin Reddit, OKCoin, which processes almost 40% of all bitcoin trades, announced to its users:

“OKCoin is currently suffering from malicious cyber attacks and as a result, some services may be suspended, Sorry for the inconvenience.”

Approximately at 3 AM users begin experiencing problems with the server and fail to access their accounts. Based on the BTC/CNY chart below, the bitcoin price begins to decline gradually around this time, and plummets at 6:30 AM when OKCoin announced to its users that some of its services have been suspended.

For a few straight hours, users were unable to withdraw or deposit funds while watching the bitcoin price fall by 9.24% percent. As a result, some users have requested the exchange to set a bitcoin bounty to catch the hackers behind the cyber attack and help resolve server issues as soon as possible.

“There is always an inherent third party risk for traders using exchanges and obviously in times of price spikes any exchange with high volumes is a honey pot for thieves,” explained Alena Vranova, Co-Founder & Director at SatoshiLabs to Cointelegraph. “I can only advise to everyone to learn some best practice like transfer only bitcoin that will be traded, never keep more than you can afford to lose, and transfer all gains whenever possible to a bank or a secure wallet such as Trezor.”