A new system designed to cross-check the identities of foreign visa-holders entering the country became operational on Monday, slowing reentry into the U.S. for many international students returning to Harvard for exams.

The United States Visitor and Immigrant Status Indicator Technology (US VISIT) system, which Congress mandated following Sept. 11, requires most foreign visitors to be photographed and to undergo a biometric fingerprinting procedure as they enter the country. Security officials check the fingerprints against a database, allowing them to identify travellers with criminal histories who may have been overlooked during the visa-application process.

The system currently exempts visitors from 27 countries, including those belonging to the European Union, who do not need visas for travel in the U.S. lasting less than 90 days. But if the Department of Homeland Security’s initiative progresses according to plan, all Europeans, too, will have to undergo similar scrutiny come October.

Travellers whose information raises red flags on the database are questioned or barred entry.

Administrators at Harvard say they cannot gauge how the program will affect the University’s international community. The University is waiting to see whether US VISIT poses major obstacles to Harvard students’ travel before taking a stance on the issue, according to Director of the Harvard International Office (HIO) Sharon Ladd.

And after just a few days of US VISIT operation at Logan Airport, no trend in international students’ experiences has emerged, she said.

“It’s a little hard to say,” she said. “How it’s going to affect our students is sort of how it will affect all international students.”

Ladd said she does not know the extent of delays caused by US VISIT.

The system currently incorporates 14 seaports and 115 airports—including Boston’s Logan International. But since many international flights transfer once in the U.S., Harvard students are feeling the effects of minor delays outside New England.

Calum Docherty ’07—who had to stop in Detroit, Mich., on his way from his home in Tokyo back to Cambridge this week—said he nearly missed his second flight due to US VISIT delays.

“It made the connection to Boston quite tight. It took them a while to get everyone through the doors,” he said.

Like several students returning to Cambridge this week, Docherty was not aware of the new program before arriving in Michigan—making for a rough reintroduction to the U.S.

Still, he says, he appreciates the need for a program like US VISIT.

“I understand where they’re coming from,” he said. “It’s just one of the things you have to live with.”

Students’ experiences with the new system varied widely, as they endured different delays and levels of scrutiny.