Nmap's Silent Partner
POF is invisible, silent and nonintrusive. Unlike active fingerprinting tools such as Nmap, POF operates only as a sniffer and generates no packets. This is extremely important, because that means it won't interfere with legitimate traffic, and it won't force you and your IDS to worry about which scans are legitimate and which are not. Since it's run on the target network, it's not particularly useful as a hacking tool--hackers will continue to prefer active scanning techniques such as Nmap.