The company told customers in a letter that it was not surprised at the result of a review, begun in October after news agency Bloomberg claimed that the supply chain had been compromised by agents from China in a bid to spy on some customers.
Reuters reported that the investigation had been carried out by a company known as Nardello & Co and Supermicro customers could obtain more details if they asked.
A source said current mainboards were tested, as also those sold to Apple and Amazon, two companies named by Bloomberg as having used the boards that allegedly had chip implants.
Towards the end of October, Supermicro president and chief executive Charles Liang sent a letter to customers, saying the story was dead wrong.
Prior to that, Apple chief executive Tim Cook took the unusual step of asking Bloomberg to retract the story which was published on 4 October. Supermicro's shares were badly hit by the story.
Amazon Web Services manager Andy Jassy backed Cook. ""[The] Bloomberg story is wrong about Amazon, too. They offered no proof, [the] story kept changing, and [they] showed no interest in our answers unless we could validate their theories. Reporters got played or took liberties. Bloomberg should retract [the story]," he said in a tweet at the time.
In its story, Bloomberg claimed security testing by Amazon in 2015 had revealed the existence of tiny chips that were not part of the original mainboard design and that this led to an extensive investigation by US Government agencies which found servers built using these boards in data centres belonging to the Department of Defence, on warships, and for processing data being handled by CIA drones.
The news agency said that major banks were also using servers made by Supermicro and that the government investigation led to several companies getting rid of the Supermicro equipment.