International flights were arriving on time and travelers coming to the U.S. were making it smoothly through the airport's checkpoints, said U.S. Customs and Border Protection spokesman Mike Fleming.
The computer malfunction, which began at 2 p.m. Saturday and lasted nearly 10 hours, prevented authorities from screening passengers arriving in the U.S. It delayed more than 17,000 people arriving from overseas.
Fleming said a computer switch failed, which knocked down the entire communications system. A backup system was in place, but it was accessible only to customs officers in some of the lanes where passengers were being processed, creating huge bottlenecks.
"We've had outages in the past, but they haven't taken nearly as long to resolve," Fleming said. "This was unprecedented in terms of impact."
During the outage, passengers were kept on planes after the terminals that normally accept international travelers became full because the previous arrivals couldn't be processed.
Though the entire system was up and running by 11:45 p.m. Saturday, it took officials until around 4 a.m. Sunday to finish processing the backlog of incoming passengers, Fleming said.