Eric: well, there s some growing concs over a social media app called tick tock, and lawmakers are worning that it could pose a threat, they think, to national security. jill january turner gillian turner explains why from washington. reporter: if you haven t heard of the latest app to go viral in the u.s., the millennials in your life definitely have. that app s called tick tock, and it s being used by nearly a billion and a half people worldwide. it s owned by china and is also sometimes used by isis. it allows users to send short and funny personal videos to catchy music. everyone from tom brady, reese witherspoon and will smith to the teenagers in your basement are using it. but now there are new worrying reports that tiktok is increasingly popular with terrorists. the wall street journal breaking news this week that isis is posting execution and torture videos on the platform. key senators on both sides of the aisle are also ringing alarm