I know what to to, if i dont want to be flooded. And of course i know that it isnt quite good to load a big file into a custom mIRC window.

Loading of the file isnt really my problem, cuz its really fast.
But opening a new thread for "searching for text in a window" would be nice.

This issue isn't just a problem of custom windows.
If i search for something on a really full and lively channel, it will also lock mIRC until the search function found something.

Applying threats to CPU intensive functions is always better, cuz it wouldn't block the whole application while the function is running.