IP spoofing is sending IP packets with a different "source" IP address than your own.

No, it cannot only be done through Unix.

IP spoofing is used by some crackers - mostly for denial of service attacks.

Obviously when your machine sends spoofed packets, it cannot get the responses to them because those go somewhere else.

Spoofing DoS (particularly DDoS) attacks are pretty difficult to stop because you can't block the packets by IP because they can have random spoofed IPs.

Some tools also use spoofed IPs, for example nmap's "Idle scan" uses spoofed IPs to bounce scans off another machine. This is clever.

Slarty