Antivirus and anti spam for ubuntu desktop

[Nils Kassube]

James Bensley wrote:
> Never say you don't need anti virus, install it but just turn it off
> if you like, to say you will never need it is naive and foolish.

Can you explain the benefit of an anti virus program that is installed 
but turned off? I would expect it to be as good as not installed but 
maybe I don't understand the magic of anti virus programs.


Nils