The scary thing about the influx of refugees into Europe is that a number of people had no paperwork at all, and some of it was thrown away along the journey. So it stands to reason that terrorists would have taken advantage of the open borders to plant themselves inside countries, like Germany, where they will be enjoying the benefits that country provides whilst planning the next attack. This is not the fault of the genuine refugees, but nobody can tell the difference.
Maybe the countries are going to have to not allow people in without paperwork?