SimpleSiteAudit anti hacker software will notify you by email of any file
changes shortly after any site intrusion occurs. You will be able to
automatically monitor all your sites from one 'Master' web site, or a local
installation of XAMPP server or similar, providing the local machine is
running 24 hours and the mail system is active. Either way, your sites can be
monitored for hacker activity without any detectable monitoring system on the
sites themselves. (in Internet)