When someone switches to GNU/Linux, one of the attributes assigned to GNU/Linux and other Open Source Operating Systems (that are free [as in freedom]) is that GNU/Linux is VIRUS or Malware free.
I have been answering (some of the misunderstandings in this respect) at multiple forums and lists, but here is the comprehensive answer.
The truthful answer is YES, writing and enabling malware executing within
GNU/Linux is possible.
I prefer the term Malicious Software
(abbreviated Malware), rather than the obscure and rather obsolete term 'Vital Information
Resources Under Siege' (VIRUS that sounds like a poorly named movie. )
