It installed 2 days ago on May 13, 2018. KB4103718
My PC is a Windows 7 32 BIT - Dell
Just like a previous SECURITY KB 4088875. this update, Once installed, when you launch Mach3 it shuts down windows and reboots.
The Fix:
Go to Control Panel > Programs > on the left click View installed updates. Then uninstall the security update. It will reboot.
Then go to...
Control Panel > System and Security and "Turn off automatic Updates"