Just like the original Trojan Horse that was built by the Greeks, the Trojan Horse Virus for your computer is actually something that is evil and bad concealed within something that seems good and positive. For anyone that might not know, a quick history lesson, the original Trojan Horse was given as a gift to the City of Troy by the Greeks who were losing the war but within this large wooden horse that was rolled into the gates of Troy was the Greek Army that came out at night when no one was looking and destroyed the city.
The computer virus variety of the Trojan Horse was first discovered in 2002 within sendmail and OpenSSH packages both included the Trojan Horse. It was done by a hijacker that broke into the distribution sites and replaced the software with his own damaged and infected ones. That is one way that your system can be given a Trojan, through software downloads and installation.
However, the most common way that users are infected with a Trojan program is through the spreading of it through emails. The sender will send it to the recipient within an email attachment that might say something like “nudegirls. jpg” or something along those lines that will make you curious and open the file.
Another increasingly popular way that Trojan Horses have been spread to users is through the ever increasing instant messenger programs such as Yahoo Messenger, AIM, ICQ, MSN messenger, and IRC. The one key to remember about Trojans is that they have to be triggered by some mechanism and will not spread themselves. For example, you can have one in your email but you do not open the link then it will not mess with your system.
A Trojan Horse, once on your system can do several things. First, it has the ability to completely take over your system and not give you access to any of your files. Next, it could possibly search your computer and monitor your usernames and passwords to various sites and even has the chances of getting your credit card numbers and sending all this information back to the creator.
The best way to keep your system from receiving any type of Trojan Horse is that of prevention. Never open files sent you by people you do not know because chances are that not only are these messages SPAM email but will contain some sort of link or file that will create a Trojan on your machine. It is fine to run anti-virus program on a daily basis but the fact is that Trojans are created so often that your definitions for viruses might not recognize the newest Trojans that have been created.
Trojans are not the kind of program that you want to speculate with so you should get your computer checked right away and continue to be leery of opening files by users you do not trust.
When not on his soapbox, Andrew Wroblewski is doing battle with the thousands of spyware programs that can affect you via his ant-spyware and spyware removal website: http://spyware.pcwash.com where you can get a free spyware scan of your computer system.