The defect was in one it calls Channel 291, the company said in Saturday’s technical blog post. The file is stored in a directory named “C:WindowsSystem32driversCrowdStrike” and with a filename beginning “C-00000291-” and ending “.sys”. Despite the file’s location and name, the file is not a Windows kernel driver, CrowdStrike insisted.

Channel File 291 is used to pass the Falcon sensor information about how to evaluate “named pipe” execution. Windows systems use these pipes for intersystem or interprocess communication, and are not in themselves a threat — although they can be misused.

“The update that occurred at 04:09 UTC was designed to target newly observed, malicious named pipes being used by common C2 [command and control] frameworks in cyberattacks,” the technical blog post explained.