But the article points that Apple wanted to protect themselves from some much more widely know threats:

"Building its own servers with motherboards it designed would be the most surefire way for Apple to prevent unauthorized snooping via extra chips.

As we've previously reported, the National Security Agency is known to intercept and modify equipment before it reaches the hands of its intended customers."

...

"The report comes as Apple fights the US government over whether it should have to write new software to help investigators unlock an iPhone used by a terrorist."

According to Bloomberg, that's how everything started:

> Apple made its discovery of suspicious chips inside Supermicro servers around May 2015, after detecting odd network activity and firmware problems, according to a person familiar with the timeline. Two of the senior Apple insiders say the company reported the incident to the FBI but kept details about what it had detected tightly held, even internally. Government investigators were still chasing clues on their own when Amazon made its discovery and gave them access to sabotaged hardware, according to one U.S. official. This created an invaluable opportunity for intelligence agencies and the FBI—by then running a full investigation led by its cyber- and counterintelligence teams—to see what the chips looked like and how they worked.

If this was true, the public denials wouldn't surprise me at all.

And if that's how the Bloomberg article had ended, with well known and previously reported firmware issues, we wouldn't be having this discussion.