It is a data integrity assurance software aimed at detecting and reporting accidental or malicious changes to data.
The following answers are incorrect :
Nessus is incorrect as it is a vulnerability scanner used by hackers in discovering vulnerabilities in a system. Saint is also incorrect as it is also a network vulnerability scanner likely to be used by hackers. Nmap is also incorrect as it is a port scanner for network exploration and likely to be used by hackers.
Reference : Tripwire : http://www.tripwire.com Nessus : http://www.nessus.org Saint : http://www.saintcorporation.com/saint Nmap : http://insecure.org/nmap