UPDATE: Super Micro says no evidence of spy chips found in its hardware.

In a letter sent to customers, the California hardware maker said a third-party investigations firm, tested its current and older-model motherboards for evidence that malicious chips or other hardware had been inserted into its products. Super Micro said it wasn’t surprised by the results.

Super Micro didn’t identify the company that conducted the investigation. Nardello & Co. later said it conducted the investigation but declined to comment further.

The investigation follows an October story by Bloomberg Businessweek that reported Chinese surveillance chips had been inserted into Super Micro hardware in order to spy on its clients, including Apple and Amazon Web Services.

Apple and Amazon have denied the content of Bloomberg’s report.

Bloomberg News declined to comment.

Bloomberg stands by its story, but more than two months later and no one has been able to find one of these mysterious chips, whose powers and abilities seem dubious to some analysts.