In a recent report published by Bleeping Computer, Microsoft confirmed it signed Netfilter a third-party driver for Windows that contains rootkit malware, a malicious collection of computer software designed to allow entry to a computer or part of its software.

While it remains unclear how the rootkit made it through Microsoft’s certificate signing process, it has been reported that it made it through the Windows Hardware Compatibility Program (WHCP) despite being connected to a Malware Command and Control Server in China.

While Microsoft said there was a small impact and that the driver did not affect the company’s users, the tech giant said it was investigating the incident and that it would refine the signing process in the future.

For more information, read the original story in Engadget.