IP spoofing

A technique used to gain unauthorized access to computers, whereby the intruder sends messages to a computer with an IP address indicating that the message is coming from a trusted port. To engage in IP spoofing, a hacker must first use a variety of techniques to find an IP address of a trusted port and then modify the packet headers so that it appears that the packets are coming from that port. Newer routers and firewall arrangements can offer protection against IP spoofing.