Trojans are programs (often malicious) that install themselves or run surreptitiously on a victim’s machine. They do not install or run automatically, but may entice users into installing or executing by masquerading as another program altogether (such as a game or a patch) or they may be packaged with hacked legitimate programs that install the trojan when the host program is executed. Hence, a user thinks they’re installing a neat, new game that they found for free, when they’re actually installing a nasty piece of software. While trojans are not capable of spreading by themselves, there have been several reports of worms that carry trojans, dropping them onto infected machines as they spread.