I am a big fan of startpage they are the only search engine I know that takes privacy seriously and easy to browse, to bypass this issue go into avasts settings, scroll down to Exclusions and click on it, then click the URLs tab, lastly enter
http://startpage.com and click add, and do the same for
https://startpage.com and click add, lastly click ok.
That should make startpage work again, I did email them and they did say there is no virus assciated with startpage.com or ixquick.com and it is a false positive, whether they where lying or not is another story
, enjoy.