Updated

The government has to do a better job of tracking down visitors to the United States who violate their visas, including identifying scofflaws faster, a Department of Homeland Security (search) report said Friday.

The Bureau of Immigration and Customs Enforcement (search) made only 671 apprehensions in 2004 after receiving 301,046 leads of possible violations, said the report from the department's inspector general. The leads, most of which come from national computer databases that track foreign students and other visitors, often don't have enough information, the report said.

One of the broadest data sources, for example — theUS-VISIT (search) program, which fingerprints and photographs foreigners when they enter the United States — only tracks departures through some ports. So the US-VISIT data does not distinguish between people who are overstaying their visas and those who left through a port that did not document their departure, the report said.

Last summer, a study by a private group that favors stricter immigration policies found that at least 94 foreign-born visitors accused of terror activity between 1993 and 2004 exploited federal immigration laws to enter or remain in the United States.

Every week in 2004, US-VISIT gave the bureau an average of 2,405 cases of possible visa violations, including potential overstays, Friday's report said.

The bureau said it will "continue to work with" the data collecting programs like US-VISIT to get better information. The bureau also said adequate US-VISIT data will not be possible until departure information is taken at all exit points.

After reviewing a sample of cases, the inspector general said it took the bureau an average of 47 days to close a file on a possible visa violator.

In cases of possible student visa violation — where, say, a foreign student may have stopped going to classes or paying tuition — the bureau took an average of 78 days to process a lead, the inspector general said, based on a sample.

The bureau responded that its enforcement unit prioritizes which leads to follow based on the level of the threat. Spokesman Dean Boyd said the unit was created to deal with high risk visa violators and "was never intended to be the sole mechanism to address all visa violators."

The inspector general also reported that the bureau closes too many cases without explaining why. Fifty-three percent of the 255 leads reviewed did not have a reason for closure — a problem the bureau said it identified in May 2004 and has already addressed.

The compliance and enforcement unit of the bureau was created in June of 2003 and has, since that date, made 1,440 arrests of high risk visa violators nationwide, the bureau said Friday.

An estimated 33 percent to 50 percent of all illegal aliens in the United States entered the country legally on visas that they violated by overstaying. The report estimated that there may currently be more than 3.6 million illegal immigrants who have overstayed visas and are living in the United States illegally.

A recent study of 94 foreign-born nationals who were either convicted or indicted on terror charges found that 22 of them either had student visas or other applications approving them to study in the United States. Another 17 used visitor visas to enter the country.

In at least 13 instances, suspected and convicted terrorists overstayed their temporary visas, said the study released in August by the Center for Immigration Studies (search), an advocate for stricter immigration policies.