I’ve been using version 4 for a while, and must admit I’m unfamiliar with the feature you are talking about. Mine updates automatically, a preset number of seconds after boot, and periodically as set by me. (That’s regarding the database updates. Or do you mean the program update?)
We are talking program updates here as VPS updates didn’t require it.
I have been using avast for almost 6 years and for the most part, program updates have always, asked for a restart.
They never did an auto restart and you could elect not to restart at that time, but of your own choosing. This hasn’t changed in avast 5.0 for me.
avast 5 has changed in that it is able to update the scanning engine as part of the virus definitions, so if there was an engine update then there might be a requirement to reboot, but I haven’t come across that yet in 5.0 as it is very early days.
I have to agree with David on this. Windows Updates has always asked whether you wish to reboot or not, depending on the updates you get. It’s customary for software, especially security software to request a reboot. You can always say yes or no. The choice is yours.
The reboot’s necessary because with very few exceptions (like, I think, the GUI), most of avast is resident as services and EXEs, and the reboot is the only way to get the updated versions into active memory. On most systems, anyway.
Generally I’ll select not now simply to give me a chance to do a “clean” logout-disconnect from my ISP and maybe also a quick last-minute check for email before doing that, and restart right after that.