AIDE is Advanced Intrusion Detection Environment, a file and
directory integrity checker.

It creates a database from the regular expression rules that it finds
from the config file(s). Once this database is initialized it can be
used to verify the integrity of the files. It has several message
digest algorithms (see below) that are used to check the integrity of
the file. All of the usual file attributes can also be checked for
inconsistencies. It can read databases from older or newer versions.