What is a Trojan Horse?
Remember the story about the ancient Greeks and Troy? Instead of the wooden horse and a bunch of soldiers a computerized trojan horse replaces the horse by a program and the pack of soldiers by malware. A Trojan horse can contain everything, ranging from a 'simple' executable file which erases your harddrives to sophisticated viruses entering you into a bot network. So a Trojan horse is nothing more, or less, then disguised malware.
Most Torjan horses serve these purposes:
- The Remote Control Trojan, which gives the creator of the trojan control over the entire computer of the victim or certain parts ie. a backdoor
- The Password Trojan, which remembers/logs every password you enter and sends it to the creator of the trojan
- The keylogger, which doesn't only save your passwords, like above, but anything you enter using the keyboard
- The FTP Trojan. This variety creates an ftp server giving the creator of the trojan no direct control over your computer, but allows him/her to browse through all your files, modify, delete or downlaod files or even to add more files
- The DDos/BOT trojan which turns your computer into a zombie used for sending spam, or atacking/infecting other computers
Since Trojan horses use specific ports to communicate, a good firewall will prevent trojans 'calling home'
You get a Trojan Horse the same way you get other malware, bad protection or unsafe surfing, to remove one, go here. And to prevent problems in the future go here.