If I've read you right, in the interface, Menu > settings > update, virus definitions and my Avast premium security are set to automatic. When I've booted up my laptop, an automatic update may happen, then I get a pop up box saying this has taken place and now I'm thinking about it, this box tells me it has been updated with a list of the features that have been updated, with this one it is informative not requiring action from me to do a restart. When I have had one that requires a restart, I've just followed the prompts, will take more notice next time one happens to see if it is an emergency update for a bug fix etc.