Koobface is a trojan that has been going around in social networking sites like - Facebook, Twitter, MySpace etc. It originally started as a Windows only trojan. But a few days ago, a new variant emerged which can infect both Mac OS X and Linux.

Infecting a Mac or a Linux system with Koobface is quite tedious. Unlike in Windows, users need to manually download a java applet and give it the permission to run - that should stop the trojan right there for most users. In Linux, it gets even better - even if the applet has been allowed to run and the system has been infected, all that is needed to stop it is a simple reboot.

However, according to some experts, the Linux infection is an unintended effect. Koobface was designed to infect OS X and because of the platform independent nature of Java, the code also runs in Linux.

This is what Jerome Segura, Security Researcher at ParetoLogic wrote:

If they really wanted to infect Linux computers, the bad guys would have added a start-up entry to ensure the code would run each and every time the machine was started. This, by the way, is not a big deal to achieve.

Rather, the code was written with Mac OS X in mind, and of course Microsoft Windows.

Anyway, this should remind people that no operating system can be completely free from malware and one of the most important factor in security is the users themselves.

Further Readings:

1. OS X the main target of new Facebook Worm?

2. New Koobface Variant Infects Linux Systems

Image Credit: The Carphone Warehouse Help Blog