Oh, absolutely. Linux, being open source, is proof against that. Any
government backdoors in the code would be found pretty quickly.

The rootkit thing, though, is not FUD (see the links below). There's a
lot of people in the AV community getting *very* worried at the idea and
a lot of money going into working out how to detect/remove/prevent such
an exploit *before* it gets loose.

But I stress - these things have yet to be seen in the wild. You really
shouldn't be losing any sleep over them.