If Malwarebytes quarantines mIRC, restoring it is just a temporary fix, because it will want to quarantine mIRC the next time too. Under settings/exclusions you can add mIRC there. For me, Malwarebytes left mIRC alone except for wanting to quarantine aliases.ini.
However, you should also beware of the knee-jerk reaction to ignore warnings about mIRC. It might not hurt to verify your mIRC hasn't been corrupted. See the command shown in
https://forums.mirc.com/ubbthreads.php/topics/261762/Re:_mIRC_crashes_from_time_to_#Post261762
if you're using version 7.51, the "ok" should be there and the hexadecimal number preceding it should be the same.
If you find the alias in the following thread reports that you have very slow disk writes, in your realtime-scan antivirus program you should probably exclude folders where mirc does a lot of disk writing to.
https://forums.mirc.com/ubbthreads.php/topics/260678/Windows_8.1_/write_very_very_v#Post260678For Microsoft Security Essentials and Windows Defender, and probably others, excluding a folder doesn't exclude subfolders below it, so you should probably exclude the folder where mirc.ini is located and also the folder where your logfiles are written.
