A Purge is one of the outcomes of a scouting report on a planet involved in The Mission. If a scouting team reports that a planet which is viable for life is in imminent danger of destruction or irreparable damage by its primary indigenous species, a "Purge Team" will be dispatched to that planet. The purpose of the Purge Team is to eliminate the harmful influence of the offending indigenous species as quickly as possible. This can be accomplished by direct intervention, invasion and subjugation, or extermination (genocide), at the discretion of the Purge Team. Purging is usually considered to be a "Last Resort" option, and is normally only considered when no other options appear to be viable.

Earth/Humanity is currently a "Purge" target, and a Purge Team is en-route.

Due to the persistent pleas of Lieutenant Commander Sil, Captain Marks has been compelled to prepare his forces for a defense of Earth against the Purge Team.