What is a Trojan Horse?

A "Trojan Horse" has come to mean any trick that causes a target to invite a foe into a securely protected bastion or place.

The Trojan Horse was a tale from the Trojan War, as told in Virgil's Latin epic poem The Aeneid. The events in this story from the Bronze Age took place after Homer's Iliad, and before Homer's Odyssey. It was the stratagem that allowed the Greeks finally to enter the city of Troy and end the conflict. In the best-known version, after a fruitless 10-year siege of Troy the Greeks built a huge figure of a horse in which a select force of men hid. The Greeks pretended to sail away, and the Trojans pulled the Horse into their city as a victory trophy. That night the Greek force crept out of the Horse and opened the gates for the rest of the Greek army, which had sailed back under cover of night. The Greek army entered and destroyed the city, decisively ending the war. 

Business

In business, a trojan horse is an advertising offer made by a company that is designed to draw potential customers by offering them cash or something of value for acceptance, but following acceptance, the buyer is forced to spend a much larger amount of money, either by being signed into a lengthy contract, from which exit is difficult, or by having money automatically drawn in some other method. The harmful consequences faced by the customer may include spending far above market rate, large amount of debt, or identity theft.

The term, which originated in New England during the 2000s, and has spread to some other parts of the United States, is also sometimes misused in reference to an item offered seemingly at a bargain price. But through fine print and other hidden trick, the item is ultimately sold at above market rate.

Some of the items involved in trojan horse sales include cash, gift cards or merchandise viewed as a high-ticket item, but the item actually being given away is made cheaply, has a very low value, and does not satisfy the expectations of the recipient. Meanwhile, the victim of the trojan horse is likely end up spending far more money over time, either through continual withdrawals from the customer's bank account, charges to a debit or credit card, or add-ons to a bill that must be paid in order to avoid loss of an object or service of prime importance (such as a house, car, or phone line).

Victims of trojan horses include those who are searching for bargains or the best price on an item, or those who are financially strapped. Many of these victims end up with overdrawn accounts or over-the-limit on their credit cards due to fees that are automatically charged.

Some of the businesses using trojan horse marketing include banks, internet and Mobile Phone Service providers, record and book clubs, and other companies in which the customer will be expected to have a continuing relationship.

Banks often offer cash initially for opening an account, but later charge fees in much larger amounts to the account holder.

Auto-manufacturers and car dealerships will often advertise free or subsidized gas to car buyers for a certain amount of time, but increase the cost of the car in other ways.

Mobile Phone companies use trojan horse marketing by attempting to sell items like ringtones to customers, who unknowingly are sold many more ringtones over time.

Computing

 In Computing, a Trojan horse, or trojan for short, is a term used to describe malware that appears, to the user, to perform a desirable function but, in fact, facilitates unauthorized access to the user's computer system. The term comes from the Trojan Horse story in Greek mythology. Trojan horses are not self-replicating which distinguishes them from viruses and worms. Additionally, they require interaction with a hacker to fulfill their purpose. The hacker need not be the individual responsible for distributing the Trojan horse. It is possible for hackers to scan computers on a network using a port scanner in the hope of finding one with a Trojan horse installed.

 Purposes of Trojan Horses in computing

Trojan horses are designed to allow a hacker remote access to a target computer system. Once a Trojan horse has been installed on a target computer system it is possible for a hacker to access it remotely and perform various operations. The operations that a hacker can perform are limited by user privileges on the target computer system and the design of the Trojan horse.

Operations which could be performed by a hacker on a target computer system include:

• Use of the machine as part of a Botnet (e.g. to perform Distributed Denial-of-service (DDoS) attacks)
• Data Theft (e.g. passwords, security codes, credit card information)
• Installation of software (including other malware)
• Downloading of files
• Uploading of files
• Deletion of files
• Modification of files
• Keystroke logging
• Viewing the user's screen
• Wasting computer space

According to a survey conducted by BitDefender from January to June 2009, "Trojan-type malware is on the rise, accounting for 83-percent of the global malware detected in the wild".
Source: Wikipedia