Super Micro Computer said in a letter to customers that it will review its hardware for any proof of malicious chips as alleged in a recent media report, and that such a hack would be "practically impossible."

"Despite the lack of any proof that a malicious hardware chip exists, we are undertaking a complicated and time-consuming review to further address the article," the company said in a letter to its customers dated Thursday.

A Bloomberg Businessweek story on Oct.4 cited 17 unidentified sources from intelligence agencies and businesses that claimed Chinese spies had placed computer chips inside equipment used by about 30 companies, including Apple and Amazon and multiple U.S. government agencies, which would give Beijing secret access to internal networks.

Super Micro denied the allegations made in the report and outlined in its letter to customers how complex such a hack would be. Super Micro stock was 3.6 percent Monday. It trades over the counter. Its common stock was suspended from the Nasdaq after the company missed several SEC filing deadlines.

Super Micro executives wrote that not only would the alleged Chinese hackers need to skirt regular testing, the unauthorized hardware would make it "highly unlikely" for their motherboards to actually function. Even if the supposed hackers were Super Micro employees rather than contractors, "no single employee or team has unrestricted access to the entire design" of their motherboards, the letter says. The letter also says it would have been difficult for companies in Super Micro's supply chain to modify motherboards because suppliers do not have access to Super Micro's full designs.

"The allegations imply there are a large number of affected motherboards," Super Micro CEO Charles Liang said in a statement calling for Bloomberg to retract the article. "Bloomberg has not produced a single affected motherboard, we have seen no malicious hardware components in our products, no government agency has contacted us about malicious hardware components, and no customer has reported finding any malicious hardware components, either."

Apple and Amazon have both denied claims in the Bloomberg report that they had found out about the chips in 2015. Apple CEO Tim Cook strongly denied the allegations of malicious hardware in its technology in a Buzzfeed News article published Friday. He also called for Bloomberg to retract the story.

Bloomberg, however, said it stood by its report and was confident of its reporting, which was conducted over more than a year.

Security experts as well as the U.S. and U.K. authorities have said they had no knowledge of the attacks.

Reuters contributed to this report.