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A four-hour outage for U.S. Customs and Border Protection left throngs of angry passengers dealing with significant delays from South Florida to Boston to Los Angeles for several hours Monday afternoon and evening.

Customs and Border Protection has nationwide outage. Expect delays in passenger processing until the system is restored. — Ft. Laude-Hlwd Int'l (@FLLFlyer) January 3, 2017

Customs and Border Protection, or CBP, said the "technology disruption" began about 5 p.m. ET and was resolved by 9 p.m. All airports were back up and running late Monday, CBP said.

"At this time, there is no indication the service disruption was malicious in nature," the agency said.

Passengers on more than 30 international flights were affected in Miami, an airport official told NBC Miami. One traveler told the station that two people passed out waiting in line.

@CustomsBorder system up & running. Will take time for passengers to be processed. Thx 4 UR patience. Many airports affected 2nite. — Miami Int'l Airport (@iflymia) January 3, 2017

Travelers took to social media to post photos and videos of the long lines and annoyed customers.

Customs line at Atlanta airport snaking around multiple wings of building. Supposedly homeland security system down pic.twitter.com/EtSMhWHQgV — Jordana Merran (@JordanaMerran) January 3, 2017

People getting hot and unhappy. pic.twitter.com/JHqyFsb9Il — John M. Phillips (@JohnPhillips) January 3, 2017

The list of airports included: Miami International, Fort Lauderdale/Hollywood (Florida) International, Hartsfield-Jackson Atlanta International, John F. Kennedy International (New York), Logan International (Boston) and Los Angeles International.

A similar but briefer failure occurred in October 2015. Customs officials blamed that episode on problems with the computers and kiosks used by passengers arriving in the country.