The National Immigration Law Center says the money is directed towards the Earnings Suspense File, which is a repository for Social Security taxes which are paid by illegal immigrants who have either used false identities, forged document or incorrect Social Security numbers.
http://www.consumeraffairs.com/news0...ret_stash.html
The U. S. government is getting the benefit of those SS payments. I doubt they're being held in any "Suspense" file. The suspense is how the U. S. government is diverting those funds to pay for something other than the SS Program - much the same as they've diverted a LOT of SS funds. If all the money paid into SS over the decades actually had stayed in a SS account, the program wouldn't be in any trouble whatsoever.