Hong Kong–based cryptocurrency trading platform OKEx announced on March 30 that it was rolling back on all futures transactions due to what executives deemed an “irregular sell-off.”

The exchange issued the following statement on its support page:

To prevent forced-liquidations due to price differences after the settlements in ‘bi-weekly’ and ‘quarterly’ futures contracts, we will rollback the transactions as mentioned, and all futures contracts will be delivered at 00:00 Mar 31, 2018 (Hong Kong Time). Further announcement will be made if there are any changes in delivery time.

The post explained that all weekly, bi-weekly and futures contracts would be fulfilled, but that after delivery, “all open orders” would be canceled and “all holding positions” would be closed at the delivery price. The incident allegedly caused the price of bitcoin to fall (albeit briefly) below the $5,000 mark on the exchange, which in turn led to “massive liquidations” and hundreds of contracts being “wiped out.”

One particularly scary moment occurred when a disgruntled user arrived at the exchange’s headquarters carrying a bottle of poison. The customer claimed to have lost nearly $11 million through the forced liquidations and threatened to take his own life by ingesting the substance.

OKEx says it always has “customers’ best interests at heart” and that the platform is “dedicated to providing the best products and technologies to protect [their] customers.” Following the sell-off, transactions were suspended for several hours, and executives issued an apology for what had occurred.

The team eventually posted a follow-up notice explaining what they planned to do in the future to prevent similar events from occurring again:

All the rollbacks have been completed. Withdrawal and Futures Trading will be resumed at 00:00 Mar 31, 2018 (Hong Kong time). In light of this incident, we are going to update our ‘Price limit rules’ for Futures Trading at 00:00 Mar 31, 2018 (Hong Kong Time) for better risk control. There will be more related improvements, and we will notify you in further announcements after they are launched.

Presently, all rollbacks have been completed and futures trading has resumed, but not everyone is convinced the problem has come to an end. Several customers are criticizing OKEx and its current systems, saying that they do not have the capabilities “to prevent what might be termed as the intended activities.” And others are suggesting OKEx may have been trying to manipulate bitcoin’s price through the liquidation, though the company has not yet acknowledged these charges.

At press time, bitcoin has fallen by nearly $700 from where it stood on March 29, and is now trading at approximately $6,700.