Tripwire : The grand-daddy of file integrity checkers
A file and directory integrity checker. Tripwire is a tool that aids system administrators and users in monitoring a designated set of files for any changes. Used with system files on a regular (e.g., daily) basis, Tripwire can notify system administrators of corrupted or tampered files, so damage control measures can be taken in a timely manner. Traditionally an open souce tool, Tripwire Corp is now focused on their commercial enterprise configuration control offerings. An open source Linux version can still be found at SourceForge. UNIX users may also want to consider AIDE, which has been designed to be a free Tripwire replacement. Or you may wish to investigate Radmind, RKHunter, or chkrootkit. Windows users may like RootkitRevealer from Sysinternals.