The thread is getting off topic. My two cents:

1. I believe that terrorist types are conducting passive surveillence of security and are probably conducting dry runs of some kind or another. I've got no proof of this other than it's what I would be doing if I were working for a terrorist organization.

2. We will never know for sure unless we either catch someone in the act (hard to prove unless they are committing a crime) or someone admits to probing security (not bloody likely).