These are old news, but I seem to have missed here in forum.
If I was not the only one, read this:
AVG Free comes packed with a bit of adware that may reflect in your search results. The modification consists in setting Yahoo! as the default search provider for both the browser search bar, as well as address bar under Internet Explorer and Mozilla Firefox. On a different note, the application can also pin a toolbar of its own in the web browser, designed to verify every link you access.Another purpose of the toolbar is that it can show the threat level of the results returned by search engines such as Yahoo!, Google, Bing, Baidu or Yandex. Worth noting is the fact that the toolbar can be disabled whenever you want and that it sports a search bar frozen on Yahoo! by default (other options are Baidu, WebHledani and Yandex).
http://news.softpedia.com/news/Antivirus-Freebies-AVG-and-Avira-140475.shtml
Shame 