It sounds like they have to know which file to look at and use Matrix Perception. What is unclear is if there is a threshold involved or if they only need a single hit. If they only need one hit, the power's strength lies that your hidden file is a needle in a haystack, that the user has to know which file to look at. But if that is the case nothing stops them from telling an Agent to inspect every single file if they suspect a Camouflaged one.