Bitmain’s hardware was at the center of a federal investigation known as “Operation Red Sunset,” according to a US official and six other people familiar with aspects of the inquiry. The investigation, led by agents of the US Department of Homeland Security, was launched to determine whether the machines could be remotely controlled for spying or to sabotage the American power grid, the official and people said. They, like others who described the federal scrutiny of Bitmain’s products, asked not to be named in order to discuss an investigation that hasn’t been disclosed publicly.

The use of Beijing-based Bitmain Technologies Ltd.’s machines at a site near a military base raised “significant national security concerns” in a federal review last year. And the firm’s name surfaced again in July in a report from the Senate Intelligence Committee that said its devices could be manipulated from China and that they present “several disturbing vulnerabilities” to the US.

Federal efforts to learn more about the machines have also included stopping some of them at US ports — although it’s unclear if the stoppages were part of the Red Sunset investigation. In some cases, investigators pulled apart Bitmain machines to test their chips and code for malicious capabilities, according to the US official and two of the people. They declined to discuss what, if anything, was found. Investigators also examined potential tariff and import tax violations, the official and people said.

In an emailed statement, Bitmain said that it’s “unequivocally false” to assert that the company can remotely control its machines from China. The manufacturer said it “strictly complies with US and applicable laws and regulations and has never engaged in activities that pose risks to US national security.” Bitmain also said it “has no awareness of or any information at all regarding any alleged federal investigation purported to be called ‘Operation Red Sunset.’”

In late March, a small publicly traded company made a surprising announcement: It would spin off part of its business into a new venture that counted Eric and Donald Trump Jr. as investors. This new company, American Bitcoin, “aims to become the world’s largest, most efficient pure-play Bitcoin miner,” according to a press release. The startup inherited options to acquire Bitmain equipment that its predecessor had arranged.

Headquartered in Miami, the company plans to build data centers in Texas, New York and Alberta, Canada, that would run 76,000 mining machines, according to corporate filings.

To begin that expansion, American Bitcoin turned to Bitmain. The industry’s dominant manufacturer, Bitmain says its products are the most efficient on the market. The rigs create new Bitcoin by solving complicated mathematical puzzles, using brute force to make trillions of guesses per second. The devices, about the size of small flat screen TVs, use tremendous amounts of energy and heat up quickly. But Bitmain executives say their machines cool down faster than others, saving miners money.

In August, according to securities filings, American Bitcoin executed a contract to buy 16,000 of the devices for $314 million. Rather than borrow money or pay cash for the machines, the company pledged 2,234 Bitcoin to acquire them. Bitmain said in its statement to Bloomberg that it had agreed to the payment structure “prior to the establishment of American Bitcoin” and that it offers such pledge payment options to many clients. The contract itself has not been made public.

“The terms of the pledge look like they may be material, and probably should be disclosed,” said Victor Suthammanont, a former senior enforcement attorney with the Securities and Exchange Commission, who reviewed the available terms of the transaction at Bloomberg News’ request.