I get this as well, it's absolutely horrible. It happens every single day, without fail, despite me having silent/gaming mode enabled and it pulls focus away from games which further proves how useless that option is.
This isn't just a notification we're talking about here either, it's a full blown, middle of the screen pop-up. The kind of thing infamous for bugging the hell out of people. One of the most despised aspects of web browsing since the internet was first conceived and now it's invading your desktop too.
I don't care if it's a free version, AVG didn't annoy me like this.