“Spoofs” your IP as another box on your ethernet segment, portscans a host “from” that ip, sniffs responses from the host. “Proof of Concept” program.
You can download it from the following link: https://packetstormsecurity.com/files/download/14256/spoofscan.c
Source: https://packetstormsecurity.com/files/14256/spoofscan.c.html