Mach 3 doesn't do that generally so it's likely to be something to do with your system, when asking questions about problems which don't impact most people and are thus unlikely to be caused by Mach3 you should really specify the versions of Mach3 and Windows you are running, whether the machine is isolated from internet and other network connections, what AV you have installed, what other software you have installed, how you are connecting to your machine etc.
Regards,
Nick