Social engineering is one of the hardest parts of the trillion-dollar online scam industry to block or disrupt.

This is the stage where fraudsters learn details about potential victims, make contact and begin to con them. And it happens mostly on social media and networking sites.

Banks, law enforcement, telecoms and technology groups are increasingly trying to join forces to crack down on the boom in fraud that's accelerated in the past few years. There's large agreement on the weak point: Platforms where criminals often find their marks need the most aggressive policing — and aren't getting it.