Estimates vary, but generally it is believed that there are 100 to 500 Linux viruses out there. The tiny number of Linux viruses that do exist have never resulted in a significant outbreak. In comparison to the plethora of viruses and worms in Windows-based platforms, the volume of Linux viruses is insignificant. So this leads us to two questions: why are there so few Linux viruses and are Linux anti-virus tools necessary?

The answer to the first question has a lot to do with the differences between Linux and Windows desktops. Linux hosts are an unwelcoming environment for a virus because the multi-user access controlled model makes traditional virus propagation methods problematic.

Let's look at an example:

Virus attacks often start with the victim receiving an email containing a malicious attachment. If the user attempts to execute the attachment on a Windows platform, it will run if it has a suitable file extension, appropriate executable content or configured to be executed by association with a particular application. Even worse, some clever Windows-based viruses don't even require the user to execute the attachment. Viruses can be activated by merely reading the email containing it. As users of many Windows-based hosts, especially Windows XP, are also running with local administration rights, the virus may potentially infect and subvert the entire host.