Matrix Perception have two uses.
1. Spot silent running networks
2. Analyze icons more in detail
Whenever you analyze a persona icon a single net hit will give you basic information, two net hits will give you more specific information and five net hits will reveal if the persona is actually a technomancer or not.
Edit. Actually, rereading RAW I am not so sure anymore

I guess this could also actually mean that you mean 5 net hits on your opposed matrix perception test to spot a living persona that is trying to hide, but in that case you are right - they would become absolute stealth monsters.