There seems to be a problem with Avast IS 6.0.1203 and Win vista 64bit Ultimate regarding Restore Points.
I realized it during current patch Tuesday. It took forever to create the restore point before applying the updates. Today it wanted to install the current defender update and hung again.
I then went on and deleted all restore points and shut off the system restore and re-enabled it (so all restore points get deleted and you start with a clean one). Same problem.
So I disabled Avast and VOILA, it ran without hanging.
Re-enabled Avast and it hung again. Something seems to be wrong there. No critical issue I guess, but it is annoying
I don't remember having these issues before 1203, but maybe I just "pushed install", did other stuff and didn't notice the hanging of the machine.