The Federal Bureau of Investigation’s refusal to discuss even the broad strokes of some of its secret investigative methods, such as implanting malware and tracking cellphones with Stingrays, is backfiring – if the goal is to actually enforce the law.

In the most recent example, the FBI may be forced to drop its case against a Washington State school administrator charged with possessing child porn because it doesn’t want to tell the court or the defense how it got its evidence – even in the judge’s chambers.

The FBI reportedly used a bug in an older version of the free anonymity software Tor to insert malware on the computers of people who accessed a child-porn website it had seized. The malware gave agents the ability to see visitors’ real internet addresses and track them down.