Department of Homeland Security (DHS) officials admitted Wednesday to a Senate committee the agency does not investigate 99 percent of the immigrants that come into the United States and don’t return to their home countries after their visas expire, according to The Washington Times.

The agency clarified their position somewhat by saying those whose names are on a list of security threats or those who are serious criminals are scrutinized, but most of the 500,000 visitors that didn’t leave at the expiration of their visas are categorized as non-priorities.

While critics are calling this a giant loophole in the DHS’s national security policy, analysts are saying it is possible that hundreds of thousands of visitors in 2015 remained in the country, and cannot be tracked as they blend into the current immigrant population.

Thousand of the visa violators are from countries that are connected with terrorists, including Afghanistan, Iraq, Iran, Libya, Pakistan, Yemen,and Syria.  The agency’s report said almost all of the 45 million temporary visas given out to tourists and businessmen between October 1, 2014 and September 30, 2015 had been honored, but the 1.7 percent who failed to return represents over 527,000 individuals.

In contrast, the government only deported 2,500 visa overstays in the previous year, and is currently investigating only about 3,000 active cases.

Senator Jeff Sessions (R-AL), chairman of the immigration subcommittee, said, “This is the way the system gets eroded. This is where public confidence is being destroyed. This is how we’re sending a message to the world that you can get away with it.”  Iowa Republican senator Chuck Grassley added when you combine the numbers of violators from previous years, the number “must be in the millions.”

Even with this new report, the numbers are incomplete, since it did not address some major visa categories like students or guest workers.  Analysts say the numbers for these categories could actually be worse, since students and guest workers tend to stay long enough to establish roots in the US.  DHS says those numbers will be available sometime next year.

Congress decreed twenty years ago that a system of biometric testing be implemented at both entry into and exit from the country, but currently only entry checks are being done.  The government depends on airline passenger information to collect the exit information.

Congressmen on both sides of the aisle are saying the time has come to solve the problem and recently dedicated $1 billion from visa fees to address the situation.