I've used and endorse it. Set it up to accept a knock sequence along the lines of: Port 38378, 1292, 65000, in quick succession. IMPOSSIBLE a port scan will ev

I've used and endorse it. Set it up to accept a knock sequence along the lines of: Port 38378, 1292, 65000, in quick succession. IMPOSSIBLE a port scan will ever hit those ports in that order. Have that sequence trigger a modification to your iptables or execute some script to modify sshd_config or whatever else. It works wonders and is another level of security.