According to the BBC, the US Customs and Border Patrol has published a Federal Register notice that would change the terms of entry for visitors to the United States arriving under the Visa Waiver Program or using the tradtional I-94 visa program. The updated application forms would ask users to identify what social networks they use and their "social media identifier" such as a username. Revealing this information would be "optional."
The proposal apparently flows from the San Bernardino hearings, where it was thought (wrongly) that the social media accounts of the shooters might have effected their admission decision. Because the new social media inquiry will be self-reported, any self-respecting terrorist could just create a false account, claim to have no account, or simply not answer.
Just this morning I wrote about the need to modernize our interdiction efforts. I am skeptical this is a useful proposal -- it will just catch the morons.