Bitcoin mining giant Bitmain is under investigation from the US Department of Homeland Security over national security concerns, according to reports.

The Beijing-based, world-leading manufacturer of crypto mining equipment has already had equipment seized at ports to perform teardowns, Bloomberg reports.

The DHS probe, known as ‘Operation Red Sunset’, was launched to assess whether Bitmain’s mining machines could be used for cyberespionage or to sabotage the US power grid.

It is feared that Bitmain’s application-specific integrated circuit (ASIC) Bitcoin miners could contain hidden kill switches or remote-access tools.

The latest investigation follows a previous warning from a Senate Intelligence Committee that Bitmain mines “are located near sensitive defense installations or critical US infrastructure such as power grids, creating several disturbing vulnerabilities.”

Bitmain’s customers include the sons of US President Donald Trump, Eric and Donald Jr, whose company American Bitcoin purchased more than 16,000 machines earlier this year, according to filings with the Securities and Exchange Commission.

The $314 million deal appeared to offer preferential access and payment terms, the SEC filings show, with Bitmain paid in “pledged” Bitcoin, rather than cash.

American Bitcoin said in a September press release that “preferential access” to Bitmain’s technology allowed the firm to “maintain a structural cost advantage."

A spokesperson for American Bitcoin said the firm “takes national security, grid stability and operation security extremely seriously,” adding that its mining operations are “isolated, segmented, monitored and protected under a rigorous security framework. Bitmain has denied any wrongdoing and labelled the allegations “unequivocally false”.

The company said in a statement that it “strictly complies with US and applicable laws and regulations and has never engaged in activities that pose risks to US national security.”

Bitmain added that it “has no awareness of or any information at all regarding any alleged federal investigation purported to be called ‘Operation Red Sunset’.”

DCD has reached out to the DHS for further information, though it typically does not comment on active investigations.