A Bloomberg article alleging that China implanted tiny microchips into the motherboards of products used by American companies has been met with fierce resistance from national security officials and businesses, calling into question the validity of the reporting.

According to the Oct. 4 Bloomberg report, entitled “The Big Hack,” Chinese spies placed the microchips on hardware manufactured by the California-based Super Micro Computer Inc. The report said that the implanted microchips affected almost 30 companies, including Apple and Amazon, in what it described as “the most significant supply chain attack known to have been carried out against American companies.”

But a growing number of companies mentioned in the report, as well as United States intelligence officials, have disputed Bloomberg’s findings.

This week, heads of Super Micro and Amazon Web Services have called on Bloomberg to retract its story. They join Apple chief Tim Cook, who urged Bloomberg to retract its reporting last week.

“From everything we know and have seen, no malicious hardware chip has been implanted during the manufacturing of our motherboards,” read an Oct. 18 letter from Super Micro to customers, which was filed to the Security and Exchange Commission. Shares of Super Micro have plunged more than 30 percent since the Bloomberg report was published.

“We trust you appreciate the difficulty of proving something did not happen.”

Officials from the U.S. intelligence community say they have seen no evidence to support Bloomberg’s findings.

“What I can’t find is any ties to the claims that are in the article,” said Rob Joyce, senior advisor to the National Security Agency, during an Oct. 10 event hosted by Real Clear Politics. He gave out a “plea out to the community” for any first-hand information that could confirm Bloomberg’s story.

“I have no leads I can specifically work … We are just befuddled.”

A spokesperson for Bloomberg told Fifth Domain Oct. 24 that “we stand by our story and are confident in our reporting and sources.”