Trojan Horse or Virus
Trojan malware cannot replicate by itself; however, if combined with a worm, the damage Trojans can have on users and systems is endless. A computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code. If this replication succeeds, the affected areas are then said to be "infected" with a computer virus, a metaphor derived from biological viruses.