Much of the discussion about illegal immigration control in the United States has centered on border enforcement and building fences along the border with Mexico. New analysis shows that nearly half of illegal immigrants came into the country legally and overstayed their visas. Among them was Zacharias Moussaoui, who has been convicted of terrorist offenses. Other suspected terrorists have done the same.

Immigrants waiting to cross the border

Every day, thousands of people wait in lines at U.S. borders and embassies.  Millions of temporary visas are issued each year to tourists, students and temporary workers. The problem is that thousands of them decide to stay in the United States illegally after their visas expire. 

Jeff Passel, demographer at the Pew Hispanic Center in Washington D.C., said about 45 percent of illegal immigrants in the United States came legally through a port of entry rather than sneaking across a border. Some used a biometric border-crossing permit called a laser visa.

Jeff Passel

Passel said, "With a population of approximately 12 million undocumented immigrants, that means 5.5 million people came in through ports of entry either with a temporary visa, or laser visas or perhaps fraudulent documents."

Passel found that the rate of overstays from European and Asian immigrants is very low. Rates from Mexico and Central America were among the highest. "It's hard to walk into the United States from India,” he said. “You have to have a way to get here and that way is with a visa."

Researchers also found that a high number of people coming across the United States-Mexico border do so with border crossing cards or other visas. These allow Mexican nationals to visit or shop with restrictions on how much time they can spend or where they can be. 

Passel said, "About 100 million times a year people use those visas, which is just a huge number. We know from talking to the people on the Border Patrol and talking to immigrants, that people are using these to come in the United States and then stay in violation of the visa."

Passel said visas are easily abused. People rent them or borrow them to come in and stay. He said collecting data on illegal immigrants is difficult. A lot of the information simply comes from statistical analysis. Passel is confident about the picture of the typical person who overstays with a tourist, student or temporary worker visa.

He said, "To get a tourist visa to come to the United States you have to basically be middle class or upper class. We think that the overstays have a different profile that tends to be more educated."

The Pew Hispanic Center says more than 30 million visa holders come into the United States by air each year. Another 150 million entries are registered through ports and land borders with Canada and Mexico. The sheer numbers, said Passel, show how difficult it is to control visa overstays.