Well any sharing site is likely to have a higher likelihood of encountering a malware/malicious link.
But if there are lots of alerts by avast users on the site with web shield, then it is possibly that information when passed to avast via the CommunityIQ function would cause the site to be added to the malicious sites list (Network Shield).
Hello,
it will be fixed in next virus definition update. It was cased by correct block of hosting IP because it redirected to one malicious .in site but there is no redirection anymore.
Jan