Pads is a signature based detection engine used to passively detect network assets. It is designed to complement IDS technology by providing context to IDS alerts.
You can download it from the following link: https://packetstormsecurity.com/files/download/34553/pads-1.1.3.tar.gz
Source: https://packetstormsecurity.com/files/34553/pads-1.1.3.tar.gz.html