While Tor theoretically can be secure (as long as you don't use it to access the clearnet), there are a few known vulnerabilities which would be trivial for an entity like the US Government to take advantage of. You can be sure there are also plenty of non-public vulnerabilities known to government security contractors and, of course, the NSA.
If you want close to guaranteed security on Tor, use PGP for all communication while connecting to it from a VPN bought with Bitcoin. Never use javascript, java, flash, etc. Use only a live linux CD and a non-standard browser. Just don't be a low hanging fruit.
Tor should still do a just fine job of protecting your anonymity if you don't, you know, shout out who you are.
You are in error sir.
Proofed(eg, OTP) or overwhelmingly messy crypto and mathematics is secure. Animal meatspace is not. Who watches the watchman? Something silicon.