Open Source Security Tool

PeerBlock is an advanced IP blocking utility

PeerBlock lets you control how your PC interacts with other computers over the Internet, letting you block servers and sites known to be troublesome or even dangerous. It lets you choose what to block, and you can also import or create your own lists.

Snort_inline - Open Source Intrusion Detection

This modified version of Snort uses iptables instead of libpcap. Operating System: FreeBSD, Linux.

AFICK- Open Source Intrusion Detection

Short for "Another File Integrity Checker," AFICK monitors changes to your file systems in order to alert you to possible intrusion. If you're familiar with Tripwire, AFICK will look and feel very familiar. Operating System: Windows, Linux, Unix.

Snort - Open Source Intrusion Detection

As the most widely deployed intrusion prevention technology in the world, Snort has earned the right to call itself "the de facto standard for intrusion prevention/detection." It performs real-time analysis to detect buffer overflows, stealth port scans, CGI attacks, SMB probes, OS fingerprinting attempts, and other attacks. Operating System: Linux, Unix, BSD, Mac OS X.