"My greatest concern is that they could be doing anything," Peter Edge, the U.S. Immigration and Customs Enforcement official who oversees investigations into visa violators, told ABC News. "Some of them could be here to do us harm."
The news comes as Prime Minister David Cameron announced plans to block British jihadists with passports from re-entering Britain as the threat of violence from the Islamic State intensifies.
The move builds on a pledge he made Monday to withdraw passports from those within the United Kingdom suspected of having traveled abroad to fight alongside terrorist groups.
According to ABC News, U.S. immigration officials have had difficulty keeping track of the escalating number of foreign students entering the United States. In the past year alone, 58,000 students overstayed their visas.
"They just disappear," Oklahoma GOP Sen. Tom Coburn told ABC News. "They get the visas and they disappear."
Since the Sept. 11, 2001 terrorist attacks, 26 student visa holders have been arrested in the United States on terrorism-related charges, ABC News reported. The 9/11 Commission had recommended that the student visa program be tightened to combat future threats but the system continues to remain vulnerable to abuse.
There are currently 9,000 institutions of higher learning which are on the government approved list certifying them to accept overseas applicants. But Congress has raised concerns that immigration officials have continued to grant schools certification even when they lack accreditation, state certification, or other measurable academic standards.
"When schools are not legitimate that enables terrorists to come here under a fraudulent basis and disappear into the fabric of society without anybody knowing that they are here for illegitimate reason," Janice Kephart, counsel to the 9/11 Commission, told ABC News.