Turning secret inadmissible evidence into legal admissible evidence seems tricky.
The only game plan I can see is this: You find out someone is up to something illegal; then you just happen have have a police officer walking by the coffee shop when you're discussing it with an associate.
No, not really. They have to show e.g. probable cause but they can happily use secret information to create serendipity: "We happened to be parked outside the suspect's location at just the right time to wittiness them talking to a known communist sympathizer."
Its not unusual for information from paid informants to get washed in this way in order to conceal their identity and prolong their usefulness.
For instance in the original example you're violating an internet law. It's not exactly something the PD can just pretend to stumble upon unless you're really careless and do it in a public place.
Even your crimes are secrets to be withheld from you.