Yeah. By complete surprise. No one could have imagined it. Four airliners were hijacked by fanatical Muslims and three reached their targets on September 11, 2001.
What could be worth hiding? Indeed.
Additional reference points speaking to the crime, the motive and means offered for consideration: AMDOCS, PTech, Odigo, ComVerse Systems, "Home Run", IAI and click here (Note: You can view every article as one long page if you sign up as an Advocate Member, or higher).