Retro-virus brought back to life

I was reading this article on Slashdot how scientists have succeeded in bringing to life an extinct virus.
After reading Jurassic Park, and the character Ian Malcolm's views on messing with stuff we don't understand, my first reaction is a little negative. Why can't we leave things that nature chose to make extinct, alone? I don't understand too much of the article, but, intuitively at least I would assume that our human body does not have resistance to viruses that we have no exposure to. So, knowing that this virus hasn't been around for millions of years, I would assume that my body doesn't have too much defense against this virus. I am trying hard not to imagine about what would happen if there was an outbreak of this virus! :-).

It will be interesting to keep see what will happen down this line in the future!