For better or worse, our views and our knowledge are influenced by our friends. For example, when someone asks me what operating system they should use, my usual response is to "use the operating system that your friends use." Why? Because if you need help with said operating system, where are you going to turn?
When you get to influencing behavior, one praise carried from friend to friend via word of mouth is worth an incredible number of online advertisements.
Of course, as the example above shows, this can sometimes backfire. My friend got this warning about Jason Allen and Amy Allen from a friend, who presumably got it from another friend, and so on. These messages often appeal to some authority - in this case, Facebook and Snopes. (Ironically, Snopes itself has said that the message is usually bogus.) At the end of the day, the only "virus" that appears is the huge number of messages passed along by well-meaning people who follow the exhortation to warn everyone about the issue.
This particular hoax is a mutation of an earlier hoax, and I'm sure that if I dig long enough I'll find a Usenet message from 2002 loudly proclaiming "Don't read Paddy O'Furniture jokes or your Unix login will be sent to a VAX at Berkeley manned by Russian spies!!!!"
