The part of the packet, message or code that carries the data. In information security, the term payload generally refers to the part of malicious code that performs the destructive operation.
(1) Refers to the actual data in a packet or file minus all headers attached for transport and minus all descriptive meta-data. In a network packet, headers are appended to the payload for transport and then discarded at their destination. In a key-length-value structure, the key and length are descriptive data about the value (the payload).
(2) In the analysis of malicious software such as worms, viruses and Trojans, it refers to the software's harmful results. Examples of payloads include data destruction, messages with insulting text or spurious e-mail messages sent to a large number of people.