_WindowServer is not a security threat itself but a regular and necessary macOS system process. It handles the graphical elements like windows menus animations, and refreshing the screen. The underscore at the beginning of its name means it's running on a special system account macOS is using. Seeing _WindowServer in the Activity Monitor is very normal, Mainly during times when apps are working on the display. Sometimes, excessive consumption of resources can be a sign of problems with software or the display, but the process itself is legitimate. In case you notice something strange first ensure that the file resides in standard macOS system files and that your system is updated.