You want to prevent a remote user at a specific IP address from connecting to your FREESCO box (or any of your machines on your LAN).
Login to your FREESCO box as root (via telnet/console/SSH). Type:
cd /rc edit rc_user
Near the end of the file, just below the spot where it says “Starting rc_user…”, type the following.
Replace <ipaddress> with the IP address you want to ban, and eth0 with the external interface of your FREESCO, if you have dialup this can f.i. be ppp0.
ipfwadm -I -a deny -P tcp -W eth0 -S <ipaddress> -o
Now, restart rc_user with the following command:
rc_user restart
The user should now be blocked from your machine.