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ISIS terrorists use a hidden smartphone app to spread propaganda and disgusting recruitment videos that include beheadings.

The app was discovered by Ghost Security Group (GSG) , a "hacktivist" collective that splintered from Anonymous and has made it a mission to disrupt Islamic State online.

Released by the Amaq News Agency - a known ISIS propaganda channel - the app features messages showing "life inside the caliphate".

This includes video speeches from terrorist leaders, reports of attacks carried out around the world and beheadings carried out by the group.

(Image: Getty)

Unlike standard apps, it cannot be installed from an app store such as Google Play.

Instead, links to it are shared privately over an encrypted messaging service.

"They [ISIS] want to create a broadcast capability that is more secure than just leveraging Twitter and Facebook," said Michael Smith II, chief operating officer at Kronos Advisory, a defense consulting firm.

“IS has always been looking for a way to provide easy access to all of the material.”

Mr. Smith explained that the terrorists use the encrypted messaging service Telegram to spread the download links for the application.

Like other ISIS social media activities, the app is used both as a way of spreading the group's message and recruiting new members.

(Image: Getty)

On the other side, Ghost Security Group, a vigilante group of hackers is trying to track down and block or remove social media accounts it believes belong to the terrorists.

So far this year it claims to have taken down 149 websites, 6,000 propaganda videos and 11,000 social media accounts linked to the terror group.