Try BlackICE Defender (Score 1)

I mentioned this in a response to another post, but I thought I'd mention it here. If you want to learn more about intrusion detection and you are running Windoze, you can buy your own industrial strength IDS for you own PC. BlackICE Defender is a full network-based IDS that has been scaled down to fit on your PC, and it comes with a built-in firewall to boot. It has some really cool features, such as:

• Easy to understand help on all the intrusions it detects. example1 example2
• Extremely high performance. The test here compares the "Sentry" version against other network-based IDSs. The "Defender" version is higher performance than other personal firewalls, but it does both IDS and firewalling.
• You can buy/download online and install it immediately without even having to reboot your machine.
• It does some simple scans against the intruders (DNS, NetBIOS) and sometimes finds out who they are.