The immigration bill being debated by the Senate would allow over two million illegal workers who received Social Security numbers prior to 2004 to receive more than $966 billion in Social Security benefits by 2040.
Despite a provision in the bill that would prevent individuals who performed illegal work and then obtained a Social Security number after 2007 from receiving credit for Social Security taxes paid in previous years, the legislation does nothing to prevent aliens who illegally obtained "non-work" Social Security numbers prior to 2004 from claiming benefits.
I don't know how helpful their statistics are, but they do seem like a legitimate organization...
UPDATE 6/17: I've been (sort of) responsible and followed up on this story! See here.