Answer: All of them.
From the BBC:
Nearly all applicants for US visas will have to submit their social media details under newly adopted rules.
The State Department regulations say people will have to submit social media names and five years' worth of email addresses and phone numbers.
When proposed last year, authorities estimated the proposal would affect 14.7 million people annually.
Certain diplomatic and official visa applicants will be exempt from the stringent new measures.
However, people travelling to the US to work or to study will have to hand over their information.
"We are constantly working to find mechanisms to improve our screening processes to protect US citizens, while supporting legitimate travel to the United States," the department reportedly said.
Previously, only applicants who needed additional vetting - such as people who had been to parts of the world controlled by terrorist groups - would need to hand over this data.
But now applicants will have to give up their account names on a list of social media platforms, and also volunteer the details of their accounts on any sites not listed.
Anyone who lies about their social media use could face "serious immigration consequences", according to an official who spoke to The Hill.
The Trump administration first proposed the rules in March 2018.
At the time, the American Civil Liberties Union - a civil rights group - said there is "no evidence that such social media monitoring is effective or fair", and said it would cause people to self-censor themselves online.
US President Donald Trump made cracking down on immigration a key plank of his election campaign in 2016.
He called for "extreme vetting" of immigrants before and during his time in office.
On Friday Mr Trump vowed to impose gradually rising tariffs on Mexico unless the country curbed illegal immigration at the US southern border.
Yes, folks, that's ALL email addresses and phone numbers an applicant may have used over the previous FIVE years, as well as ALL social media profiles (from the article it's unclear whether the five-year thingy applies or not).
Let me repeat that.
If you ever wish to apply for a US visa and you're not a certified Trump worshipper (who are we kidding here?), you're going to hand over:
ALL PHONE NUMBERS
ALL SOCIAL MEDIA PROFILES
That includes your Tinder and Grindr profiles, your totally-forgotten email address you used one time to access a certain website, your porn usernames, your anything and everything. Do not comply, and the authorities shall seek fit to deny you entry or kick you out, whichever is funnier to them, because how is abuse under this going to be corrected politically?
... yes, this may be the policy equivalent of Stephen Miller splooging all over the Statue of Liberty in an eerie reprise of that scene in End of Evangelion.
(And you will not convince me that this is not a Miller Pride & Joy -- if he didn't have a hand in this policy, that's logically impossible.)
Discuss.