Hundreds, or possibly even thousands might have already reached the European Union by now. In the past five months time, some 60,000 "refugees" have arrived at the EU via Libya. Many of the important ports, such as Sirte, Nofilia, and Benghazi are under solid Islamic State control, for many months now (see the map below).
I suspect this is just more fear-mongering from the scared anti-muslim/immigration types. I doubt there's any or if there is they probably wont or cant do much. And what exactly makes IS any different from any other muslim extremist that might already be in europe? It's not like they're trained assassins. They're just you're average terrorist not some super-boogeyman.