Apparently that "updater" tool is trying to access something online, and it's not equipped with a timeout. That's not exactly good design.
Unfortunately, this leaves your system in a "stuck" state, as that step will never complete unless you log off or reboot. After that, I wouldn't bet on the efficacy of the installed software.
One possibility: If you use the mvps.org hosts file, it's possible you're blocking a "parasite" web site that Avast's "updater" tool depends upon (don't think too hard about that if security concerns worry you) - thus the program hangs. Try temporarily renaming your hosts file to hosts.ref and see if the updater will succeed.
-Noel