It's fairly easy to turn off updates, and somewhat more difficult to turn off security updates, for reasons that should be self-evident. These updates that are still occurring are probably of the latter variety.
I'm running F17 and Gnome 3.4, and have also disabled all automatic updating. The security option is in a dconf key. You'll need dconf editor installed. If you have something else, KDE, XFCE or what-not, then I'm afraid I cannot help you.