In The Night of the Living Dead , zombies sucked brain matter in a frenzied hunger. In the computer world, Trojans can be used to turn your PC into their own computing matter - effectively turning it into a zombie machine. Once under the control of such an illicit program, the Trojan can be accessed by hackers possessing the master, or server, version of the Trojan. The compromised machines can then be used for any number of things. In other cases, however, the intent is much more ominous.
Trojans have the same right on the system as does the logged in user.
In other words, if the user can, the Trojan can. This includes deleting or modifying files, installing other software, uninstalling software, or sending sensitive password and login information to a remote server. Computers affected by Trojans can be used to launch attacks against targeted Internet sites. By having thousands of computers accessing the same site at the same moment, the site servers can sometimes become overwhelmed and may no longer be able to process requests. DDoS, attacks, are becoming increasingly common.