Checking infinite loops may not be a hard science, but you could use a script loop check similar to the way browsers work these days, with an alert dialog popping up after considerable time saying "This script is running slowly, should I stop it?"-- this would probably be quite helpful to those unaware of ctrl+break.
mIRC could actually take advantage of the nature of the program to echo "You have a slow running script press CTRL+BREAK to stop it" in the active window (force a display update) instead of using an alert dialog, if it wanted.
The main problem with infinite loops is that users are unaware of the key combination to break out of them. mIRC could implement feasible solutions that have already been proven to help.
