The United States government has started asking a select number of foreign travelers about their social media accounts.

The news came on Thursday via Politicoand was confirmed to Mashableby a spokesperson for Customs and Border Protection (CBP) after the new procedure reportedly began earlier in the week.

The process dovetails with what has been expected for months and has been slammed by privacy advocates.

Here's what we know about the basics of the program.

Whose information is the agency collecting?

CBP is asking for social media info from anyone traveling to the U.S. through the Visa Waiver Program, which means they'd be able to travel about the country for 90 days of business or pleasure without a visa.

The social media request is a part of the Electronic System for Travel Authorization (ESTA) form, which travelers looking for a visa waiver have to fill out before they get to the U.S. The form is used to assess "law enforcement or security risk," according to the CBP's website.

Travelers from 38 countries are eligible for a visa waiver, including those from the United Kingdom, Belgium, France and Hungary.

What kind of information are they looking for?

The form reportedly asks for account names on prominent social networks such as Facebook, Twitter, YouTube, Instagram and LinkedIn, as well as networks many people don't think much about, such as Github and Google+.

Is it mandatory?

No one has to fill out their social media information to get into the country, and CBP has reportedly said it won't bar anyone from the U.S. just because that person didn't want to give their Twitter handle to the government.

That said, privacy advocates have decried the policy, since many travelers are likely to fill it out just in case. A number of groups including the ACLU signed an open letter in October warning of the forthcoming changes.

"Many of these travelers are likely to have business associates, family, and friends in the U.S., and many of them will communicate with their contacts in the U.S. over social media.

This data collection could therefore vacuum up a significant amount of data about Americans’ associations, beliefs, religious and political leanings, and more, chilling First Amendment freedoms."

Why do they want social media information?

The U.S. has long tried to spot radicals and radical sympathizers online, especially anyone affiliated with the Islamic State (ISIS).

ISIS has long had a prolific and disparate social media presence, especially on Twitter, which they've used to spread messages and recruit those who might be hundreds or thousands of miles away from fighting in Syria and Iraq.

Initially, government officials wanted ISIS sympathizers to keep tweeting, because agencies were able to gather bits of information from those tweets. Then, however, the government got tired of how many ISIS members and sympathizers there were on Twitter and other platforms, so they ramped up pressure on those social networks to shut down such accounts.

For the government, this is the next step in working out which potential travelers to the U.S. have "connections" to ISIS. Of course, it's unclear what language the CBP would find alarming, and whether their alarm bells would be warranted.

How long will they hold onto the information?

Assuming the social media information will be used just like the rest of the information on the ESTA form travelers have to fill out for a visa waiver, the Department of Homeland Security will keep it readily available for up to three years after it's been filled out. Then the information is "archived for 12 years," but still accessible to law enforcement and national security agencies.

Can they share the social media information with others?

Homeland security and the CBP can share your social accounts with "appropriate federal, state, local, tribal and foreign governmental agencies or multilateral governmental organizations responsible for investigating or prosecuting the violations of, or for enforcing or implementing, a statute, rule, regulation, order or license, or where DHS believes information would assist enforcement of civil or criminal laws," according to the CBP website.

In other words, assuming the social information is treated like all the other information they collect form those with a visa waiver, homeland security could potentially share it with any law enforcement agency on the planet. They just have to "believe" the information might be of use in solving some type of legal violation.

So once you type out your Twitter handle and send in the application, that information is hardly yours.