If a spying player has a higher Espionage Technology level than the target planet/moon there could be a chance that the spying mission is not noticed by the target.

This could be scaled based on a number of factors.

The player notices that a spying mission has taken place at a specified planet or moon but does not see from where the spy mission occured.

The player notices that a spy mission has taken place but cannot see which planet was spied nor from where the mission occured.

The player does not see that a spy mission has occurred.

The chances could be scaled on the difference in espionage technology level and on the number of espy ships both being used by the aggressor and the number of espy ships present on the planet or moon being spied.

This sounds okay at first, but the more I think on it, this would just be too overpowered. This would mean we could never tell when the top players are online because when they spied us, we would never see it, or we would never see where they were.

I like this idea.

But if target have more then 100 esp probes on planet/moon I don't see how he can't see that someone is spying his planet/moon.
- @DrLot: The player does not see that a spy mission has occurred. [ This can't happen]

Rest is ok even if there is many ship on planet/moon. Of course there is a chance of destroying the probes. If that happen the person u spying should then see from where the probe came.

The question is how big should be that difference in esp technology. I suggest 4-5 level difference.