A group of unidentified people broke into cryptocurrency exchange OKCoin’s Beijing office yesterday (October 23) by breaking elevators and smashing doors, according to a post by the company on Chinese microblogging platform Weibo.

OKCoin said the group threatened its staff and vandalized its office. The company called the police, who took the alleged vandals away.

Prior to the incident, OKCoin reported that a group of unidentified individuals had been hanging around its office. The company said the individuals refused to identify themselves, but they claimed that they were OKCoin users. The company speculated that they were hired to disrupt their operations.

According to 8BTC, a bitcoin and blockchain information platform, the violence is as a result of futures trading provided by the platform, in which users experienced forced liquidations and irregular transactions.

OkCoin claims to be the world’s biggest digital asset trading platform. Following China’s ban on cryptocurrency trading, the company is now based in San Francisco, California. The company lost its CEO Chris Lee in May who joined its competitor Huobi, another crypto trading company hailing from China which recently completed a backdoor listing in Hong Kong.

This is not the first time OkCoin has had an incident at its Beijing office. In March, an investor threatened to commit suicide by drinking pesticide at OKCoin’s office in Haidian after losing a total of  RMB 11 million ($1.6 million), including money he borrowed from his own company’s shareholders.

OKCoin founder Xu Mingxing (known as Star Xu) has been accused of fraud and irregular account management, as well as offering false investment information and promising unachievable returns. Xu has also been accused of intentionally blowing up investment accounts in option-like OKCoin products and derivatives.

In September, Xu was summoned by the Shanghai public security organs investigating alleged fraud connected to cryptocurrency. Authorities in China have been taking illegal cryptocurrency trading seriously in recent months, banning events, removing content related to cryptocurrencies, and blocking payments to overseas exchanges.

A day prior to the break-in at the company’s headquarters, Xu published a Weibo post and criticized “some” media’s “illegal stalking” in Beijing. Media and investors were reportedly planning a stakeout outside a Marriott hotel in Beijing’s Chaoyang District, where Xu was rumored to be residing.

Xu’s team also criticized its rival Huobi for maliciously organizing attacks and reports.