Writing your own port scanner using netcat

While attackers utilize the proxying application and Tor network, it is also possible for them to write their own custom network port scanner. The following one-line command can be utilized during penetration testing to identify the list of open ports just by using netcat:

while read r; do nc -v -z $r 1-65535; done <iplist

The same script can be modified for more targeted attacks on a single IP as follows:

while read r; do nc -v -z target $r; done < ports

The chances of getting alerted in any intrusion detection system using custom port scanners is high.