Apple has strongly refuted claims made in a Bloomberg feature that allege the company’s data centers may have been compromised by tiny chips secretly installed on its servers by Chinese spies.

It’s a wild story, and one that took the news by storm last week with its bold convictions that motherboards made by Chinese manufacturer Supermicro could have been compromised by spy chips. These motherboards are used by a wide range of companies, but most notably by two trillion-dollar tech giants: Apple and Amazon.

Both have refuted the story, as have Supermicro, and all three have been backed up by both the UK National Security Center and Homeland Security in the US, who say there is “no reason to doubt” Apple’s statement. All signs point to Bloomberg being wrong here. The publication says it has multiple sources, but all are anonymous eyewitness accounts without concrete proof.

Apple says it keeps a close eye on its data centers for any kind of unusual activity precisely to avoid this kind of thing, and it has found zero evidence that any of its servers have been tampered with, let alone managed to “phone home” to China with any kind of secure information.

Still, it’s a serious claim and one with the potential to be quite damaging to Apple’s reputation. As such, the company has penned a letter directly to Congress refuting the claim and explaining more about how its many security protocols work to prevent malicious hardware manipulation.

It’s rare for this kind of correspondence to go public, but if you’re curious you can read the entire three-page letter in full here.