1.) He changes the "joke" so that someone's system who wasn't catching it - might think it is a new joke. ... this person takes the time to keep the virus moving.

2.) DATS are just DATA FILES - some have a .DAT extension - but not all of them. They simply attach data to an applicable file/ program. Right now there are over 50,000 viruses in the Norton data file.

1.) That is part of what I was referring to when I mentioned it does come back. From my experience though it is most likely getting transfered by your being in someones book rather than someone just sending it to you. Once it is sent out there and is in some server it just spreads itself. It is identifiable though when you look in your mailbox and see the email of the sender. Also as a general rule, delete anything that starts with Snow White or The Dwarf's etc.

2.) That is I assume another way of referring to the "Virus Definitions" that you update when you do a "Live Update". You are updating the .dat and other files that tell Norton what to look for and how to analyze files for the various known viruses.