Charles Liang, the company's president and chief executive, said in the letter that "no one has shown us a motherboard containing any unauthorised hardware chip, we are not aware of any such unauthorised chip, and no government agency has alerted us to the existence of any unauthorised chip".
Liang's denial comes soon after Apple chief executive Tim Cook took the unusual step of asking Bloomberg to retract the story which was published on 4 October. Supermicro's shares were badly hit by the story; they fell from US$21.40 to US$12.46 and are yet to recover, hovering around the US$15 mark.
Amazon Web Services manager Andy Jassy said in a tweet on Tuesday that Cook was right. "[The] Bloomberg story is wrong about Amazon, too. They offered no proof, [the] story kept changing, and [they] showed no interest in our answers unless we could validate their theories. Reporters got played or took liberties. Bloomberg should retract [the story]," he wrote.
@tim_cook is right. Bloomberg story is wrong about Amazon, too. They offered no proof, story kept changing, and showed no interest in our answers unless we could validate their theories. Reporters got played or took liberties. Bloomberg should retract. https://t.co/RZzuUt9fBM— Andy Jassy (@ajassy) October 22, 2018
The news agency said that major banks were also using servers made by Supermicro and that the government investigation led to several companies getting rid of the Supermicro equipment.
A few years ago, the same journalists, Jordan Robertson and Michael Riley, wrote a story, claiming that the US Government had prior knowledge of the Heartbleed bug, a serious vulnerability in OpenSSL, before it was announced. Bloomberg did not issue a follow-up after the story was denied.
Apple issued a detailed denial when the story was published. Later, its former general counsel, Bruce Sewell, said that the FBI had told him it had told him it had no knowledge of any probe into such an incident, as claimed by Bloomberg.
And the company took the additional step of writing to the US Congress denying the story. Chief security officer George Stathakopoulos said in a letter that the company had found no evidence to justify the claims made in the Bloomberg report.
Liang said in the letter: "Our motherboard technology involves multiple layers of circuitry. It would be virtually impossible for a third party, during the manufacturing process, to install and power a hardware device that could communicate effectively with our Baseboard Management Controller because such a third party would lack complete knowledge (known as 'pin-to-pin knowledge') of the design.
"These designs are trade secrets protected by Supermicro. The system is designed so that no single Supermicro employee, single team, or contractor has unrestricted access to the complete motherboard design (including hardware, software, and firmware)."
He added: "Each of our contractors has only the portion of the total engineering design of the motherboard that it needs to carry out its part in the manufacturing process.
"Modifications to the design plan must be confirmed with Supermicro, which then passes those modifications on to those downstream in the manufacturing process.
"If any single contractor attempts to modify the designs, the manufacturing process is structured so that those alterations would not match the other design elements in the manufacturing process.
"This makes it practically impossible for anyone to add an unauthorised hardware component that could both escape detection and function properly. This also ensures there are multiple quality checks built into each step of our manufacturing process."
Liang said for these reasons, he was confident that Bloomberg's allegations were wrong.
"...experts across the ecosystem, including FBI director Christopher Wray, NSA senior cyber security adviser Rob Joyce, director of National Intelligence Dan Coats, the Department of Homeland Security, the UK’s GCHQ and even an expert quoted in the article itself, have questioned these allegations. Finally, Apple and Amazon have issued strong statements denying the claims," he said.