In the 6-minute, graphic video, the al-Qaeda-linked group celebrates the 2013 Mall attack that killed more than 60 people in Kenya. The video's narrator ends it by calling for more shopping mall attacks.
Former FBI agent Andy Arena says, "Law enforcement and intelligence community are out there doing their best, but the reality is that the threat is there."
While some malls are tightening security, Arena says this problem isn't going to go away, adding that social media has only made the potential for threats worse.
Any mall is vulnerable, Arena says.
The biggest threat is what you don't know, but law enforcement is gathering intelligence daily.
"If there is someone locally who has been radicalized, law enforcement is doing their best to catch them before they do anything bad."