A technique used by crackers to gain unauthorized access to computers and from which newer routers and firewall arrangements can offer some protection. IP address spoofing is accomplished when the cracker sends messages to a system with an IP address identifying these messages as originating at a trusted host.
To spoof an IP address, a cracker must first use a combination of methods and tools to identify the IP address of a trusted host and then change the packet headers so that it appears as though the packets are coming from a trusted host.
Jupitermedia Corporation. What is IP Spoofing? [Online, April 14, 2004.] Jupitermedia Corporation Website. http://www.webopedia.com/TERM/I/IP_spoofing.html.