What amounts to a proof-of-concept trojan horse application for the Mac started circulating around the Internet on Thursday. Ambrosia Softwareis Andrew Welch detailed the trojan, which he dubbed the "Oompa-Loompa Trojan," in the companyis support forums. The malware-style application attempts to trick unsuspecting users into thinking that it is a JPEG image. If launched, the application requires administrator access before it can install files that attempt to send copies of itself to people that are in your iChat Buddy list.

This unsophisticated proof of concept is not a virus, and does not take advantage of any security flaws in Mac OS X. It also relies on features in Tiger (Mac OS X 10.4), so it is likely that certain parts of its code canit operate on Mac OS X 10.3 and earlier.

Computer security company, Sophos, has named the trojan horse "OSX/Leap-A," and is advising Mac users that use virus protection software to make sure that their virus definistions are up to date.

Trojan vs Virus
A trojan horse is an application that tricks users into thinking it is something other than what it really is. For example, someone could write an application that deletes the files from your Documents folder, but give it name and icon that leads you to believe it is a collection of photos from a friend, an application updater, or some other "friendly" application. Although a trojan horse can take advantage of security weaknesses in your computeris operating system or other applications, it doesnit necessarily have to.

A virus, in contrast, is a self-replicating application that attaches itself to documents, applications, or your operating system, and usually takes advantage of security flaws in your applications and operating system. In most cases, a virus is used maliciously to cause damage to your computer, or to use your computer for other acts without your knowledge. That can include stealing information from you and your data files, using your computer to launch attacks on other computers over the Internet, and to propagate itself to other computers.

Both Trojan horses and viruses are considered malware.

To date, there are no known viruses for Mac OS X.