Chapter 15 Unified Threat Management for FortiOS 5.0 : Security Profiles overview : Security Profiles components : Intrusion Protection System (IPS)
  
Intrusion Protection System (IPS)
The FortiGate Intrusion Protection System (IPS) protects your network against hacking and other attempts to exploit vulnerabilities of your systems. More than 3,000 signatures are able to detect exploits against various operating systems, host types, protocols, and applications. These exploits can be stopped before they reach your internal network.
You can also write custom signatures, tailored to your network.