If ever move the cursor ofver the avast icon in my icon tray, whether by accident or not a green (or sometimes red) box will appear on the screen just above the notification tray with the message "You are Protected"
When you pass the mouse cursor over ANY icon in the tray or taskbar
a tooltip popup will appear with a short description, status info, etc.
That's default Windows behaviour.
The Avast/AVG popups may be a little different in that they are coloured,
and a little larger than most. However, some other icons will also yield
a popup holding several line of info. For example the Keyboard language.
I'm not aware of any Windows settings option to disable this behaviour,
either globally or application-specific.