Allow User Abort [off]
should manage that for you.
Thanks Phil, Should this be the first step in my script, or after freeze window?
It should be the first step. Until it executes, user interaction (such as pressing escape on a windows system), could abort the script. But in practical terms the "eyeblink" between when your script starts executing and when it freezes the window is too short to make any practical difference in the results.
Two other comments on "allow user abort". If you have FileMaker Advanced, you can still use the debugger to abort such a script. This can be a major life saver if your script goes "rogue" and you need to abort it but can't. It's also why I do not enable this option for a script until after I've tested it and am confident that it is working correctly.