6
cache is still used in templates_c for theme files, fyi (default function of XOOPS it seems)
check your raw http logs, see if anyone is touching your files from the outside somehow
btw, if someone has access to your files from within the server (i.e.- another user's account), it might not matter if you set it to 444, just a though
make sure you report this to your provider, it could be that other user directory is malicious or has written a script that is somehow affecting the whole server.. not sure of the possibilities