Bloomberg published an article on Thursday 4 October claiming that an attack by Chinese spies invaded 30 US companies, including Apple and Amazon. It said that a tiny microchip was planted on servers used by the companies and was discovered in 2015.
However, Apple and Amazon have both strongly denied such a chip was found.
"We are deeply disappointed that in their dealings with us, Bloomberg's reporters have not been open to the possibility that they or their sources might be wrong or misinformed, said Apple in a statement.
"Our best guess is that they are confusing their story with a previously reported 2016 incident in which we discovered an infected driver on a single Super Micro server in one of our labs. That one-time event was determined to be accidental and not a targeted attack against Apple."
Amazon's response was shorter but carried the same message: "We've found no evidence to support claims of malicious chips or hardware modifications," it said.
The original article claims that tiny chips were found on motherboards supplied by Chinese server company Super Micro. It too has denied the allegations.
Neither Apple nor Amazon uses Super Micro for its servers today, but both say their switch to other manufacturers were unrelated.
Officials familiar with the investigation told Bloomberg that the chips discussed could have been used to open backdoors for hackers: "Hardware attacks are about access," one revealed.