Defense) will offer a reward chosen randomly from a drop table, including but not limited to mods. Modules obtained are randomly chosen for every player.
Typically if a mod drops from a specific enemy: The usual mod drop chance is 3% (can be doubled with Mod Drop Chance Boosters), but may differ depending on the type of enemy. Drops from enemies: Almost all enemies have a chance of dropping a mod, selected from their drop table (visit their respective pages for more details).