IP Spoofing is a technique which is used to gain unauthorized access to computers, whereby the squatter sends messages to a computer with a false IP address to indicate that the message is coming from a trusted host. In other words it is a process of returning IP address that is different from the one that is actually assigned to the destination website.
To involve in IP spoofing, the intruders use a variety of techniques to find an IP address of a trusted host and then modify the packet headers so that it appears that the packets are coming from that trusted host.
In case IP spoofing is used to hijack a browser, whenever any visitor types in a legitimate site’s URL, he is taken to a fraudulent Web page of the intruder. For example if the intruder has spoofed a popular ecommerce website, then any Internet user who would type in the URL of that particular site would be redirected to the spoofed content created by the intruder.
If a user interacts with dynamic content on that spoofed page, the intruder can gain access to sensitive information on the particular computer or network such as a credit card number or password, or install malware.
IP Spoofing is a big no no when in terms of SEO as it is considered a black hat seo technique. Newer routers and firewall arrangements can help protect your network from these malicious cloaking and cracking techniques.such as IP spoofing.