There is absolutely no backdoor in Tor.
We know some smart lawyers who say that it's unlikely that anybody will try to make us add one in our jurisdiction (U.S.).
If they do ask us, we will fight them, and (the lawyers say) probably win.
We will never put a backdoor in Tor.
We think that putting a backdoor in Tor would be tremendously irresponsible to our users, and a bad precedent for security software in general.
If we ever put a deliberate backdoor in our security software, it would ruin our professional reputation.
Nobody would trust our software ever again - for excellent reasons!
But that said, there are still plenty of subtle attacks people might try.
Somebody might impersonate us, or break into our computers, or something like that.
Tor is open source, and you should always check the source (or at least the diffs since the last release) for suspicious things.
If we (or the distributors that gave you Tor) don't give you access to the source code, that's a sure sign something funny might be going on.
You should also check the PGP signatures on the releases, to make sure nobody messed with the distribution sites.
Also, there might be accidental bugs in Tor that could affect your anonymity.
We periodically find and fix anonymity-related bugs, so make sure you keep your Tor versions up-to-date.