Apple, Amazon, and Supermicro each released a forceful denial that their systems were tampered with following the publication of a Bloomberg Businessweek report last week, which alleged that Chinese agents introduced microchips into servers manufactured in the country. In a letter to Congressional officials, Apple reiterated its denial, saying that it has found no sign of tampering.

Reuters obtained a letter written by George Stathakopoulos, Apple’s Vice President for Information Security, which he sent to the commerce committees for both the US Senate and US House. In it, he says that “Apple’s proprietary security tools are continuously scanning for precisely this kind of outbound traffic, as it indicates the existence of malware or other malicious activity. Nothing was ever found.” He also reiterated that Apple hadn’t contacted the FBI over such an issue, as alleged in the report, and indicated that he would be available to brief Congressional staff in the coming days.

In its original statement, Apple said that while Bloomberg Businessweek asked the company to comment on the allegations in recent months, it “conducted rigorous internal investigations based on their inquiries” and hadn’t found any evince of tampering. Beyond each of the company’s respective denials, US and UK governmental agencies have backed them up, each saying that they have no any reason to doubt their statements.