Anybody that thinks "open" or "closed" borders (whatever that means in globalised international society) will prevent, or even reduce, this form terrorism is clutching at straws.
This war kicked off around the time of the first crusade and it won't be done until the human race has gone.
It's part of our world and we have to live it, just as we have done for most of human history.
If you are looking for measures to better manage it, we had a bunch of those just last week over here - enhanced legislation to monitor communications of all kinds. Big brother is watching, because big brother has to. We have to tolerate intrusion into our private communications, because that is one of the only effective ways to catch these medieval retards before they commit their acts.
I feel for France today - I have many friends living there and it's a great place full of wonderful people.