And you thought your holiday hangover was rough.

Monday night, a temporary computer shutdown of U.S. Customs and Border Protection systems at airports across the country led to major headaches for travelers nationwide.

People returning home from the New Year's holiday weekend were being processed at international terminals by hand at some airports, resulting in long lines and short tempers. Travelers reported issues in Chicago, Boston, New York City, Baltimore, Miami and Atlanta, among others.The outage lasted for four hours, the Customs agency said in a statement late Monday, before the system was up and running again.

"U.S. Customs and Border Protection is experiencing a temporary outage with its processing systems at various air ports of entry and taking immediate action to address the technology disruption," the agency said in a statement Monday night. "CBP officers continue to process international travelers using alternative procedures until systems are back online. Travelers at some ports of entry are experiencing longer than usual wait times and CBP officers are working to process travelers as quickly as possible while maintaining the highest levels of security."

"U.S. Customs and Border Protection experienced a temporary outage with its processing systems at various airports today beginning at 5 p.m. EST and ending at approximately 9 p.m. EST. All airports are currently back on line," the agency said. "CBP took immediate action to address the issue and CBP officers continued to process international travelers using alternative procedures at airports experiencing the disruption. Travelers at some ports of entry experienced longer than usual wait times as CBP officers processed travelers as quickly as possible while maintaining the highest levels of security.



"During the technology disruption, CBP had access to national security-related databases and all travelers were screened according to security standards. At this time, there is no indication the service disruption was malicious in nature,” the agency said.

Even though the outage was resolved, the Customs backups were likely to take awhile to ease.

About 10 p.m. Monday, Miami International Airport said its system was back online but said it would take time for passengers to be processed.

Travelers took to social media to vent, beg for help and share photos of massive lines and wall-to-wall weary passengers.

Michelle Sencibaugh, a K-12 teacher in St. Louis, was returning from a 12-day holiday trip to the Caribbean island of Curacao when she slammed into a nightmare of chaos and confusion at the Miami airport.

"I've never seen anything like it," Sencibaugh told USA TODAY. "No one was giving us direction. They didn't tell us what was going on. It was just a herd of people."

Sencibaugh said the situation grew increasingly frightening as the colossal crowd she estimated in the thousands became agitated. She said there were people in wheelchairs, people with young children, one man who said his pregnant wife was starting to bleed — all crammed together at the terminal.

"People started to pass out, people were screaming, shoving each other with luggage," she said. "People were scared, absolutely."

Sencibaugh, who said she didn't learn there was an outage until she found reports on Twitter and Facebook, eventually made it through Customs via Global Entry, clearance for pre-approved travelers. She said others were likely to be in line for five or six more hours.

Follow Susan Miller on Twitter: @susmiller