However, the new version of Avast antivirus 5 free edition displays advertisement about their pro version on the main window.
If you think this ads is annoying, there is a simple solution by Techtrickz.com (my sister site) to block the ads. This tip is for Windows 7 with default Firewall.
In windows 7, run Windows Firewall and select Advanced settings, then click Outbound rules and choose New rule.
Now select Custom at the bottom and click next button. Then select "This Program Path" and browse to Avast install directory and choose AvastUI.exe and click next button.
Now click next, next to get Action window. Here make sure that bottom rule is selected and click next.
Here make sure that all profiles - domain, private, and public - are selected and click next. Now just enter any name and description for your rule. Finish your settings and restart your PC.