A method for detecting computer viruses comprising three phases: a decryption phase, an exploration phase, and an evaluation phase. A purpose of the decryption phase is to emulate a sufficient number of instructions to allow an encrypted virus to decrypt its viral body. A purpose of the exploration phase is to emulate at least once all sections of code within a region deemed likely to contain any virus present in the target program. A purpose of the evaluation phase is to analyze any suspicious behavior observed during the decryption and exploration phases to determine whether the target appears to be infected.