We need targeted surveillance and by that I mean something that many will vehemently disagree with. Before you down vote, please make the effort to read to the end and then down vote!
If I was a doctor and my patient had cancer in his foot, then if try to treat the foot to get rid of the cancer. I would also pay particularly close attention to the leg connected to that foot, to make sure that the cancer did not spread throughout the entire body.
With that in mind, I believe that our only choice, assuming we want our free and open societies to remain as they are, is to monitor all Muslims living in Europe who have the potential to be radicalised and turned cancerous. Warrant, judge, monitor.
We could try and close all the borders (they are porous) or we can make pointless suggestions, like we should kick all immigrants out of our countries, but the fact remains that the attackers in London and Paris earlier in the year (and I'm betting last night too) are second or third generation immigrants who were born in the west.
Since 9/11 the security services have tried to crack down on radicalization within the internal Muslim communities, by expelling radical clerics, but the internet allows the radicalization of the very young and marginalised youth (mostly boys), to continue. This isn't surprising considering the racism against immigrants in the ghettoes of Paris, and the exclusion of these youths from French society. First came the riots in 2005, and now something much more sinister has arrived.
Or societies are desperately trying not to impose draconian rules of monitoring on a religious group, but as it stands I see little choice in the matter.
Also Germany is facing a firestorm. Within the large numbers of genuine refugees, are Syrian fighters from both sides. Some are most likely disillusioned by the brutality of ISIS, and some are coming to watch the world burn. We desperately need to know who these people are and urgently before they disappear into the masses.
We also need to understand ISIS and what they are trying to do. Wikileaks recently published a document [1] that outlines their goals and they are simple. They want to achieve the Islamic State with pure Sharia Law. Moderate Muslims (aka "the greyzone") either have to join, or be burnt in the war with all other Kafir (that has been prophesied). They need the west to turn against their Muslim communities forcing them back to fighting and into the open arms of ISIS. They want those new immigrants in Germany to be excluded, treated like dogs, so that they either return to the middle east and (re)join the perverted form of Islam that is preached by IS.
Now you can see the dilemma that the west faces. On the one hand, logic dictates that they need to closely monitor the youths in Europe who are getting radicalised over the internet, but they can't single out a religious group without a severe backlash. The alternative is to monitor everyone on the internet, because in doing that you get to watch the small part that you are interested in, without appearing to religiously persecuting Muslims.
Finally, there is a twitter account [2] that follows radical militia fighters from Syria and the middle East. A large number of which are now posting photos of them in Europe now. We need to find them now.
[1] ISIS strategy in France: Provoke a crackdown on Muslims to "Eliminate the Grayzone" https://t.co/8fb8BbKOG2 #ParisAttacks #AttaquesParis
[2] https://mobile.twitter.com/EU_MilitiaWatch/