How many terrorist incidents has TSA credibly prevented? The answer is zero.
Do you think a government agency would just publicly blast all the unsuccessful attempts that were prevented, without fear that future criminals can look at those attempts and do better next time by learning how to avoid making the same mistakes?
Disclaimer: I agree with most of the posters that TSA is mostly just a security theater. But just because I think so, that doesn't make the flawed parent argument any better.
Surely those statistics can be verified by, say, the House Committee on Homeland Security without needing to leak the details of specific attempts.