The FBI has recently notified law enforcement agencies that al Qaeda could use suicide bombers to blow up public buildings.
This is always a possibility but I would imagine al Qaeda wants to destroy very high profile buildings that are guarded better than most (I would hope).
What interested me about the story was the point made by the terrorists that many publicly accessible buildings have poorly trained or unarmed security guards. And it reminded me of local shopping malls and the security guards I see there. Looking them over with a critical eye, they don't make me feel secure at all; quite the opposite. I imagine if real terrorists attacked, they would be in big trouble and so would the customers, such as myself.
Al Qaeda could have done something like this by now but they haven't. It isn't such a desirable scenario for them.