I merged other beliefs and mine together. There are those on the internet that believe the SSN is the 'mark of the beast' of the anti-christ (system). Myself, I am not claiming that. I believe it to be a mark of a beast, the beast being you or I.
666 part is a theory of mine that 666 could represent any number combination like our current notation of XXX. If this is true, then XXX-XX-XXXX would be the same as XXX or 666; just a larger signature.
I could even take this a step further and say that I believe the word beast includes any heathen. If that is true, then this covers all non-believers, covenant breakers, idol worshipers (American Idol anyone?).