Do spies perform counter espionage?

[Akadah]

Do spies perform counter espionage? Basically, do they increase my chances of catching opponent spies coming into my cities? If so, is it better to place them in cities or along the borders?

 

[blitzkrieg1980]

If you fortify them in cities, they act like a Security Bureau. So yes, they perform passive counter espionage on the tile they are on. When you build a Sec Bureau, however, the effect does NOT stack.

I place them in all my major cities. However, if you are very tech heavy and most other civs are behind, putting a spy in all cities will help prevent someone from stealing a tech.

 

[nbcman]

@ Akadah

As blitzkrieg1980 has said, spies do increase the chance of catching opponent spies. For a full description of the spy detection mechanic, check out Bhruic's spy detection thread.