<i>Is it? How many attacks has it prevented?</i><p>This. So now I&#x27;m curious and I found this posting by Bruce Schneier at <a href="https:&#x2F;&#x2F;www.schneier.com&#x2F;blog&#x2F;archives&#x2F;2008&#x2F;01&#x2F;how_well_see_so.html" rel="nofollow">https:&#x2F;&#x2F;www.schneier.com&#x2F;blog&#x2F;archives&#x2F;2008&#x2F;01&#x2F;how_well_see_...</a> which is relevant. He points to some data that really indicates that it just doesn&#x27;t actually lead to preventing terrorist attacks at all.