Espionage is the act of using spy probes to spy on a planet to determine its total resources and possibly defences and technology levels. The most important factor for espionage is the espionage tech research. The amount of information received is determined by the difference in research level between the player sending the probe and the one whose planet it is, as well as the number of spy probes sent. However, each spy probe sent increases the chance of the espionage being detected by 1%.[1] For instance, when 20 probes are sent, there is a 20% chance of detection. If espionage is detected the opposing player will receive a counter espionage report which details from which planet the spy probes were sent.

If the player and the spying target have the same espionage tech level, the following information will be received with various numbers of spy probes[2]:

1 spy probe Show resources only
3 spy probe Show resources and ships
5 spy probe Show resources, ships, and defenses
7 spy probe Show resources, ships, defenses, and buildings
9 spy probe Show resources, ships, defenses, buildings, and tech levels

However if they are a level above you, you need an addition level (the next odd number) of probes to show the same information. Spy probes might also randomly be destroyed in an espionage attempt and it is believed that this is when a counter-espionage report is generated.