The Department of Homeland Security has managed to lose more than 6,000 foreigners that entered the country on student visas. These students reportedly arrived in the U.S., stayed the duration of their visas and never returned home.

The students have since disappeared. In the past year alone, 58,000 students overstayed their visas, according to ABC News. Of these, more than 6,000 were selected by agents for follow-up because they raised heightened concern.

"They just disappear," Sen. Tom Coburn (R., Okla.) said. "They get the visas and they disappear."

Their status exploits a gap in homeland security that was supposed to be fixed in the wake of the September 11, 2001 terror attacks.

As the threat of Islamic national armies rises, experts fear the gap in security may make the U.S. vulnerable to terror attacks — especially since the 9/11 hijackers entered the country on student visas. The man who drove the van containing explosives into the World Trade Center garage in 1993 was also a student visa holder.

Since 9/11, 26 student visa holders have been arrested on charges related to terrorism.

"It's been pointed out over and over and over again and the fact that nothing has been done about it yet… it's a very dangerous thing for all of us," said Thomas Kean, 9/11 Commission co-chair. "The fact that there's been no action on this is very bothersome."