A proxy for the number of Illegal Aliens?

With Illegals using others Social Security numbers, it would be interesting to know what percent of these cases involve illegal aliens. They might all use the ever popular 000-00-0000, but some might get other numbers.

Imagine filing your tax return and learning that someone else got your refund. With your name and Social Security number, no less.
The IRS is grappling with a nearly five-fold increase in taxpayer identity theft between 2008 and 2010, a Government Accountability Office official plans to tell a House hearing Thursday. There were 248,357 incidents in 2010, compared to 51,702 in 2008.
The GAO findings, obtained by The Associated Press, don't begin to describe the pain for a first-time victim, who must wait for a refund while the IRS sorts out which return is real and which is a fraud.
Many identity thieves don't get prosecuted, according James White, director of strategic issues for the GAO..
"IRS officials told us that IRS pursues criminal investigations of suspected identity thieves in only a small number of cases," White says in testimony prepared for a House Oversight and Government Reform subcommittee. . . .
"We want to know why this problem is apparently getting much worse," said Rep. Todd Platts, R-Pa., chairman of the subcommittee. "By bringing these issues to the public as quickly as possible, the committee hopes to give citizens the necessary information so they can protect themselves from such identity theft." . . .