World's biggest ponzi scheme? Not even close - social security is obviously the biggest. And unusual for two reasons:
1) The promoters do not (generally) lie. Rather, they simply don't go out of their way to let investors know that current contributions funding distributions to historic participants.
2) To some extent, the promoters are actually trying to make the system somewhat legit (actuarially feasible) - rare to unique in ponzi world.
Just teasing. Sort of.