Definition: A Spoof, as it relates to information security, relates to a person or system’s identity being substituted with another. The word refers to any one of a number of specific attacks. IP packet headers, for example, can be altered to include the IP source address of the imposter. A cracker can insert a malicious email address. The same is true of web site URLs. A cracker can fool the target into thinking that he or she is a trusted or legitimate source. The attacks are so sophisticated that a counterfeit page can be made to look like the real thing.