This article originally appeared on watchdog.org.
WASHINGTON, D.C. ??? As America???s colleges resume classes, thousands of foreign students with expired visas are no-shows.
The Department of Homeland Security says 6,000 of them represent a national security threat, but the DHS admits it has no idea where they are.
While the 6,000 are considered subjects of interest, DHS says it has lost track of 58,000 foreigners who entered the U.S. on student visas.
???They just disappear,??? U.S. Sen. Tom Coburn, R-Okla., told ABC News. ???They get the visas and they disappear.???
Most of the 9/11 hijackers were in the U.S. on expired student visas. Coburn said that since those attacks, the government had arrested 26 foreigners with student visas for terrorism-related activities.
As for the rest?
???My greatest concern is that they could be doing anything,??? said Peter Edge, an Immigration and Customs Enforcement official. ???Some of them could be here to do us harm.???
Experts say the government???s admitted inability to track student visas exposes economic and educational concerns, too.
???Over and above any security worries, DHS does not pay attention to the mild accreditation standards of its sister agency, the Department of Education, and permits the operation of schools that are not accredited by DoE-recognized entities,??? David North, a policy analyst with the Center for Immigration Studies, told Watchdog.org.
???As a result there are visa mills that continue to ???teach??? ???students??? in cases where the schools should be closed and the students sent home,??? North said.
???Nominally in charge of all this is the Student Exchange Visitor Program ??? one of the sleepiest federal agencies in existence,??? he said.
John Miano, a New Jersey lawyer and former tech worker, debunks the notion that out-of-status foreign students are landing high-paying jobs and displacing their college counterparts.
???Clearly, overstays are a large part of the illegal-alien population,??? Miano told Watchdog. ???It appears to me that illegal immigration is the largest force that businesses use to drive down wages of the low-skilled workforce.???
Donna Conroy, director of Bright Future Jobs, an advocacy organization for tech employees, said foreign nationals holding student visas may participate in the federal Optional Practical Training program for high-skill workers.
But despite widely reported surveillance activities by the National Security Agency, Conroy said ???there is no tracking mechanism to monitor and audit??? students who overstay their visas.
At a Senate Homeland Security Committee hearing in 2011, Sen. Rand Paul, R-Ky., re-raised the possibility that foreign students could pose national-security threats.
The Republican senator???s concerns were validated after Azamat Tazhayakov, a student from Kazakhstan on an expired visa, was implicated in the Boston bombing.
???If we had a more competent visa program, we might have prevented 9/11,??? Paul said.