It's well known that undocumented immigrants often present false or borrowed identification, including Social Security cards and numbers, in order to find work in the underground economy. But there is a side to this story that is seldom explored: How the Social Security taxes paid by these workers aren't reclaimed as benefits, at least not by those who make the payments. This unused money makes for a substantial amount that helps keep the trust fund afloat.

Perhaps this is why a great piece that appeared in the Washington Post over the weekend keeps making the Twitter re-tweet rounds. In the piece, syndicated columnist Edward Schumacher-Matos shares an interview he did with a top Social Security official as part of a book project, during which he learned that the estimated contributions to the Social Security trust fund from unauthorized workers' wages are much higher than previously thought. He writes:

In response to a research inquiry for a book I am writing on the economics of immigration, Stephen C. Goss, the chief actuary of the Social Security Administration and someone who enjoys bipartisan support for his straightforwardness, said that by 2007, the Social Security trust fund had received a net benefit of somewhere between $120 billion and $240 billion from unauthorized immigrants.

That represented an astounding 5.4 percent to 10.7 percent of the trust fund's total assets of $2.24 trillion that year. The cumulative contribution is surely higher now. Unauthorized immigrants paid a net contribution of $12 billion in 2007 alone, Goss said.

Previous estimates circulating publicly and in Congress had placed the annual contributions at roughly half of Goss's 2007 figure and listed the cumulative benefit on the order of $50 billion.

The Social Security trust fund faces a solvency crisis that would be even more pressing were it not for these payments.

Undocumented immigrants are unable to claim Social Security benefits, although rumors to the contrary that have been circulated online, including in the form of a petition.