Asked to explain those practices, Koskinen replied, "What happens in these situations is someone is using a Social Security number to get a job, but they're filing their tax return with their [taxpayer identification number]." What that means, he said, is that "they are undocumented aliens … . They're paying taxes. It's in everybody's interest to have them pay the taxes they owe."

As long as the information is being used only to fraudulently obtain jobs, Koskinen said, rather than to claim false tax returns, the agency has an interest in helping them. "The question is whether the Social Security number they're using to get the job has been stolen. It's not the normal identity theft situation," he said.