Bro: A System for Detecting Network Intruders in RealTime.
You can download it from the following link: https://packetstormsecurity.com/files/download/51887/Bro-A-System-for-Detecting-Network-Intruders-in-RT.pdf
Source: https://packetstormsecurity.com/files/51887/Bro-A-System-for-Detecting-Network-Intruders-in-RT.pdf.html