In the hands of a human player vs the AI that is? I just played a game where I had a crap starting spot but went on with it anyway, being very much behind in production, science and culture. Once again I started checking the victory screen too late and by the time I did I noticed China was two modules away from a science victory. I hadn't even researched let alone build a spaceport... I had one spy at the time and China had 3 spaceports. Long story short: I pumped out enough spies to cover them all, kept all three cities in disarray with sabotage and rebels and won out a science victory in the end. Not one spy killed or captured, 2 or 3 times caught but escaped. Is this another tactic that the AI can't defend against?