AIDE (Advanced Intrusion Detection Enviornment) is a tool to check the file integrity. It is an opensource substitute for TRIPWIRE. It allows to take snapshots of all the major configuration files, binaries as well as libraries stats. It helps to find which binaries have been changed in case of compromisation of the system.

Nice little tool I have just started to play with it and so far no problems, Baldy

Linux Security Notes – AIDE File Integrity