Recently in my game I got an SM message about a particular system having one or more alien fleets or colonies in the system. The only problem is that this particular system is one that was explored a long time ago by my PC race, and one that is on a major trade/supply route, so ships go through there all the time. There's only two other races, and neither have jumped into that system.
What triggers the game to think that there's an alien fleet or colony, and how do I tell it to stop it? Basically I am planning to ignore the message.