Well the purpose varies from person to person
I personally collect to experiment with them- Working and exploring virii gives you an idea about various programming tricks/techniques, plus we get to know a lot of the OS, the many ways our OS can be vulnerable.. Using this knowledge we can prevent any virus to infect in the first place (infact currently im not using any a/v)
Plus the sheer fun of it, and for *Bragging* rights
Btw, know this about virii: A virus is harmless unless and until we activate it. Just because I'm having the virus on my computer doesnt mean that it
infected my computer. A virus is not some extraordinary thing- its just another program/script.
Of course, one could by mistake click on the virus and infect the comp- which is why I password protected each and every virus so that it cannot infect my comp accidently and intentionaly.
And when I have to run/execute the virus and watch it 'live' in action, I just use a Virtual Computer (Microsoft Virtual PC / VMware). Whatever happens in the Virtual Computer doesnt affect the real computer, so we can experiment to our hearts content..
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