The four 'dreaded' letters on airline boarding passes that travelers say they never want to see

Should you panic when you see "SSSS" printed on your boarding pass? Social media users are going viral for sharing their experiences after noticing the four letters upon arriving at the airport.

So, what does SSSS mean if it appears when you check in?

"It stands for 'secondary security screening selection,' and it's a measure implemented by security authorities in the U.S. to screen certain passengers with additional checks."

"Selectees for this enhanced security are chosen in the days leading up to a flight when airlines share the manifest with U.S. security authorities," Griff added.

Griff said that most people who receive SSSS before a flight will not be able to check in online, and will receive a printed ticket from an agent - this is exactly what happened to Jordyn Verzera and JT Mocarski, creators of the travel blog "The Mobile Homie.""

Whenever they receive the SSSS on boarding passes and post it on social media, users flood them with questions in the comment section.

Verzera and Mocarski told Fox News Digital about what this additional screening process entails.

The first time Verzera and Mocarski encountered the four letters, only one of them was able to check in before their flight.

Verzera attempted to get her boarding pass on the airline's app, but a notification popped up saying she had to check in with a gate agent, she said.

Verzera said she was confused until she spoke to an agent.

Verzera said that every item she packed had to be removed from her luggage, including her toiletry items. Those items were then laid out on a conveyor belt where everything was swabbed. Her laptop also had to be turned on in order to go through security.

"It was a little intimidating the first time around," she said.

Verzera had to arrive early at the airport to receive her boarding pass and had to wait in line for three hours. She said it took her another hour to go through the additional screening in customs.

Griff agreed with Mocarski's point by adding that it depends on  the airport you are in, with some requiring an early arrival and a "complete paydown." Some airports may require a "personalized interview, along with more screening."

Mocarski thinks social media may have slightly villainized the extra security measure, he said.

"At the end of the day, it's random, like even the TSA agents, it's not like they're picking you. They know the remedies that they have to go through to make sure that they're doing the check," Mocarski said.

Griff said you might receive the SSSS for a variety of different reasons: "suspicious travel patterns like frequent one-way international trips, or many visits to high-risk countries," he said.

"SSSS can also be entirely random, and there's no way to know when booking your flight whether you'll be chosen as SSSS," Griff added.

Verzera said people might be concerned about "SSSS" as they feel the extra screening will lead to them missing their flight.

She and Mocarski recommend getting travel insurance for this purpose.

They also said that when "SSSS" appeared on their boarding passes, the plane "waited" and didn't leave any "SSSS passengers" behind.

"I think for us, and something we like to remind our friends of, is that travel isn't perfect," Verzera said.

"You grow the most when you're uncomfortable with travel - just understand that this happens. Just roll with it, and just let it be part of your day . . . go through it, and then [say], 'I hope it never happens again.'"

A TSA spokesperson told Fox News Digital via email that SSSS is meant to accomplish the agency's "transportation security mission." 

"Security measures begin long before passengers arrive at the airport," the spokesperson wrote. "TSA works closely with the intelligence and law enforcement communities to share information. Additional security measures are in place from the time passengers get to the airport until they arrive at their destination. In some cases, passengers are randomly selected for enhanced screening."

No traveler is able to bypass the screening, according to the TSA. 

If a traveler experiences difficulties getting through the security screening process, they can reach out to the DHS Travel Redress Program for assistance.

Visit tsa.gov to learn more.