system
2
Avast shields,in your case it was network shield, just saved your computer from being infected,you will get that page you showed in screenshot only when you click more details. ;D
The Main moto of avast shields is to prevent you from getting infected and it does that by aborting the connection and blocking the infection right away when its a case of web based attack and then the infection cant touch your machine ;D
If you right click on the avast ball in your tray and hit show last pop up message you can re-review the last popup alert from avast.