EVE Online is one of the few MMOs where players in guilds (corporations and alliances) have some valid concerns about spies from rival groups infiltrating their ranks. The concept of being a spy or saboteur is a profession of sorts that arose in the game. There aren't any game mechanics that necessarily enable spying or make it into a viable profession, nor are there any rules that prohibit most of these activities.
Wes from EVE Tribune recently wrote a piece called "Metagaming", dealing with how espionage can impact rival corporations and alliances in EVE. Wes asks, "Why is everyone so paranoid about spies and metagaming?" then goes on to explain how espionage in EVE works, categorizing spies by their modus operandi: