Directory size

Hi, I would like to know if webmin has some possibility to control if some file in some directory folder has changed,
I thought that OTHER - SYSTEM AND SERVER STATUS - DIRECTORY SIZE would have this ability, but it doesn’t seems to work.
I am the only owner of the webmin, nobody else use it and I would like to be assured and I want to be warned if some file in the root has changed or if some folder has changed a size, Knowing this I would be immediately warned that something has happened to the files (maybe hacked)
I have setup maximum size 10kb in public_html folder, and I get no warnings even if I change more than half of the file(30-100kb)
How does this service work, what can I do in order to be informed when something happens to my files, when hacker add some codes, when hacker upload some malicious files, change and append new codes?
I would be interested about every change in public_html root files, because I am the only one who works with files, who deletes, who change and install and appends new codes, if this happen in another time when I worked on it, I would be sure that it is something what nobody wants there and at least I would immediately know what exactly has changed and when. Till now only notice I very often get is that the Directory service monitor goes down and not that something has changed.