ISIS supporters have gloated about sleeper cells nestled in Europe which are poised to carry out horror attacks on innocent civilians.And most frighteningly of all - terror experts have backed up the chilling claims. During the migrant crisis it was feared jihadists could sneak through the European Union’s porous borders as thousands arrived into the continent daily from war-torn nations. This included in July, Mohammad Daleel, a 27-year-old failed asylum seeker, who blew himself up outside a party in Ansbach, Germany. ISIS later said he was a "soldier of the Caliphate".