A Trojan Horse is a program designed to cause destruction but deceives itself as a unsuspicious program. However, unlike a typical computer virus or worm, Trojans do not copy themselves or multiply within the file system, but they can still be as harmful. The term Trojan Horse is derived from the Ancient Greek story of the wooden horse that was used to help the Greek army invade the city of Troy by stealth, hence the programs getting installed without the user knowing.

Trojan horses (usually called Trojans for short) are very similar to spyware in that they get installed unwittingly by the user, usually within a legitimate program or disguising itself as an unsuspicious.  If installed or run, a Trojan will generally be granted full access to the machine.  From here the program has a lot of potential to cause damage to the file system, but this depends on the motives of the developer, which typically consist of:

• Money Theft or Ransom
• Data theft
• Remote access, spying and surveillance
• Destruction
• Using the machine as a resource

Another common practice of a Trojan Horse is to infect multiple computers within a computer network, also known as a botnet.  This could be a major issue within a business environment causing dramatic consequences such as huge down time, resulting in loss of revenue.  The Trojan can also attach itself to an email client sending out bulk emails, spreading the virus (providing it’s opened and run) to all of the user’s contacts.  Again, within a business this could mean thousands of emails getting sent out, spreading the Trojan very rapidly, which could be great news for the Trojan creator if it’s motives are to collect credit card information.