1. Network Intrusion Detection Systems (NIDS): These systems monitor the network traffic for malicious activity. Examples include Snort, Suricata, and Bro.
2. Host Intrusion Detection Systems (HIDS): These systems monitor the activity on a single host or device. Examples include OSSEC, Samhain, and Tripwire.
3. Wireless Intrusion Detection Systems (WIDS): These systems monitor wireless networks for malicious activity. Examples include AirDefense and AirTight.
4. Application Intrusion Detection Systems (AIDS): These systems monitor applications for malicious activity. Examples include ModSecurity and AppDetective.
5. Database Intrusion Detection Systems (DIDS): These systems monitor databases for malicious activity. Examples include Oracle Advanced Security and Imperva SecureSphere.