virus free??

I suggest reading this:

http://en.wikipedia.org/wiki/Linux_malware

and this:

https://help.ubuntu.com/community/Antivirus

I don't think you can say that there are NO viruses on the Linux platform, but I DO think you can safely say that there are 99% LESS viruses in the wild for the Linux platform than on the various Windows platforms. This difference in virus numbers means that Linux is simply a lot safer to use than Windows. Just my opinion.

And, the level of privileges applied to users. Simply tinkling the system configurations requires an elevated permissions for changes to commit. Users are bound to work on a limited environment - their home directory.

And be note using open source we don't have no malware no spyware no backdoors...

And be note using all open source coming from trusted origin (repository) we don't have malware, spyware, backdoors...

When Unix was designed, it was for multi-user environment and by a network company, so Unix was designed originally with security concerns, not like Windows which was conceived for lonely PC without network.
Another reason is there is less users of Linux than Windows.
And even if Linux is used for valued server, Linux's people are not supposed to be as naive as Windows ones.
So it means it is less costly to attack Window's computers than Linux computers.
(But remember the first virus written was for Unix!!).

Check this link, has a very good and thorough explanation.
http://linuxmafia.com/~rick/faq/index.php?page=virus