Virginia TV shooting: Facebook, Twitter and others grapple with dark side of instant sharing

As posting, linking and streaming videos online become more immediate, the Virginia shooting highlights a growing challenge among social media companies that try to crack down on users who promote violence online, experts say.

Even as one violent video or account comes down, another pops back up. "The Internet is inherently more difficult to control because it has several gatekeepers," said Rita Cant, a legal fellow at the Center for Democracy & Technology's Free Expression Project. Facebook, Twitter and Google-owned YouTube all have rules against promoting violence on their sites, but with billions of videos uploaded every day, the companies heavily rely on their users to report harmful content.