Ok well, to start with let's define a good virus, and a bad virus.  A
good virus would be a virus which would be seen to have a beneficial
effect.  For an example in this article we'll use a virus that infects all
files and on execution checks to see if, in turn it has been infected by
another virus, if so it notifies the user and doesn't run the program.

    A bad virus, well a bad virus doesn't have to be one with destructive
code.  We'll count any virus that doesn't do something "good" as bad.
Makes sense?  Hehe.. I thought so.  Usually good viruses are custom made
for companies or sold as a package.  Much like experimental virii they tend
to escape their habitat and infect the innocent home PC users out there.

    Joe Blow has a computer literally full of viruses!  He is infected to
the brim and luckily not one of them has any (purposely) destructive code
in them.  He doesn't use scanners because he can't be bothered and his
computer works fine.  Great!  This guy is a perfect platform for virii to
spread, no doubt most of his friends are the same and no one knows they're
infected.

    After a while Joe gets hold of some hot warez off a mate that works in
a big company, he found it on their hard drive.  So Joe runs the warez and
in turn spreads this "good" virus all over the place.  Next bootup Joe has
a message telling him his computer is infected.  He then shits himself and
formats his hard drive.  Bummer about that says Joe, and gets back to his
usual warez rampaging.
                                                                              
    Ok, so that was a bit extremist.  Ah well.. not only was a cool site
for the spreading of viruses destroyed.  Joe lost all the warez he'd been
collecting for months!  That, I guess is a very non believable circumstance
so I'll move along onto something else :).  To understand further why there
is such a kick about good viruses, we have to know exactly what most people
think the word destructive means.
                                                                              
    To me a virus that overwrites random sectors with the word "lamer" side
by side is destructive.  So is formatting random tracks and labelling them
bad sectors.  A viron is destructive!  Well here's a side that not everyone
has thought about (I haven't, so I'm not sure whether it's true or not).
When a virus infects a file it changes the structure of that file.  Thus
making the warranty on the software void.  This is damage, which can then
give people the right to call viruses destructive.
                                                                              
    A virus can't spread without modifying executables in some way, voiding
the warranty/rights to a package.  So every virus is destructive!  Bummer
that.  Ah well.. we all have our own thoughts on what virii are.  Virii
should spread, that is the initial function of most.  If people want to use
them to harbour "good" code then this is their decision, but why bother?
Surely there are easier ways of having this code executed.
                                                                              
    Viruses are what the author intended them to be.  Different authors
intend different things.  "It is not known what this virus does besides
replicate," does not really help tell the public what they are.  Companion
viruses don't modify executables, but I guess not every file is EXE.
Whatever.. viruses are good and bad.. that's life!
                                                                              
    Metabolis