There are two very big issues on America's plate in 2013; A) what to do with Social Security (SS) , and B) immigration. For the most part, these two topics are uniquely different. There is one important area where they lap over - money.
SS maintains an account called the Earnings Suspense File (ESF). This is account used for booking money that comes into SS from improper SS ID# (SSNs). Credits to ESF can arise from administrative errors. It's easy to imagine how some one transposes a few digits on the SSN, and the computers at SS recognizes the mistake. Until the error is fixed, the money from payroll taxes on that SSN is suspended in the ESF.
The ESF is not just an account where errors are trapped and later reconciled. It is a doghouse account that has collected well over a hundred billion dollars over the past decade. The vast majority of the money in the ESF comes from workers who are using an illegal SSN.
This site produced the following report on the Earnings Suspense File (ESF) at SS: