The United States government is exploring the idea of incorporating visa applicants' social media activity into the background check process, in a bid to prevent extremists from entering the country.

The visa screening process has come under review by the Homeland Security and State departments, after it emerged that one of the shooters in this month's San Bernardino, CA, attack had immigrated to the United States on a "fiancé visa" - and that she has posted troubling evidence of radicalization on social media long before she was approved for the visa.

Republican Senator Richard Burr said Sunday in an interview on CBS that evidence from social media suggested Tashfeen Malik, a Pakistani national, supported "Islamic jihad" as early as 2012 – two years before she received a K-1 visa to the United States in 2014.

While there are now currently several test programs underway on how to "incorporate 'appropriate' social media reviews," according to the Associated Press, ABC News quoted a former official as saying that any review of social media accounts by immigration officials had been forbidden under a department policy in 2014.

Despite widespread calls by politicians to do so, it's not clear how any such policy to review social media activity could be implemented in an effective way.

Malik herself used an alias along with strict privacy settings that would have required Facebook to release the data even if authorities were aware of her pseudonym, according to CNN.

On top of the fact that Facebook and Twitter both require a court order to release users' private data unless there is an imminent threat – and its unlikely a court would issue a blanket order considering the more than 9 million visas issued per year – extremists planning an attack are unlikely to be posting on social media publicly under their own name.

Any review of public social media activity as a part of the visa process seems destined to snare only travelers posting political dissent about the United States - and potentially having an extremely chilling effect on free speech for those with business or family interests in the country.