Planemike
The next time you are at an airport take a look at around, could you spot a potential terrorist, or are all asian males suspect. I think not. It has to be done by a process of elimination and spotting 'hostile reconnaissance' is just one way of doing it.
Who would have thought that Richard Reid (the shoe bomber) would have tried to do what he did but someone paying attention caught him out.
The attack on Glasgow Airport by, of all people Doctors, must have had a trial run and reconnaissance carried out before the attack.
Richard Copeland who carried out the nail bombing on the Pub in Old Compton Street was a white British male, but that Pub could easily have been the terminal building at Gatwick or Heathrow.
All I am saying is everybody needs to get used to the authorities asking what they are doing at certain times & locations. You are never going to stop it.