How does it work?

I have been sabotaged, and have sabotaged a few times. Most of them, there was a spy defending that was "exposed".
When I was sabotaged my spy was on "alert status" and he didn't stop the sabotage anyway.
So I've never seen a succesfull counter espionage action.
Why is that? Is the chance of detecting spys very little?
Does it increase over time?

Does anyone know exactly how that works?

When you put your spy over one of your ops/colonies/relics, click the op/colony/relic and click the eye. Then click 'Add Spy Protection', for 20 energy you can get 50 spy protection. You lose 1 spy protection every tick, so it's best to keep it high. If you have more spy protection than the enemy spy has infiltration points, you will capture the enemy spy and be safe from spy attack.

Great!
Thanks!