Here’s a quick summary of NPC rats you might encounter that I wrote up for another player a while back:
Since I wrote that, the Triglavian Invasions have now been added as well. You will be notified if you enter an Invasion system. These rats will swarm you, consistently respawn and have much better AI than the others, so be particularly careful in dealing with these.
And, as others have said, avoid using Autopilot as this is just a magnet for disaster.