1. An apparently harmless program containing malicious logic that allows the unauthorized collection, falsification, or destruction of data. 2. A program containing hidden code allowing the unauthorized collection, falsification, or destruction of information. 3. A computer program with an apparently or actually useful function that contains additional (hidden) functions that surreptitiously exploit the legitimate authorizations of the invoking process to the detriment of security. For example, making a "blind copy" of a sensitive file for the creator of the Trojan Horse.