spp_portscan.c – Snort Portscan Preprocessor logs port scans through snort.
You can download it from the following link: https://packetstormsecurity.com/files/download/17143/spp_portscan-0.2.9.c
Source: https://packetstormsecurity.com/files/17143/spp_portscan-0.2.9.c.html