With an upgrade in the last 24 hours or so to avast Free 6.0.1203, Network Shield has started blocking access to files on Yahoo Groups. An example message:
Malicious URL blocked
URL: f1.grp.yahoofs.com/v1/sP89TlM2sINjXK7M3KWCwAH08Hj-qCh0wBnLDetlIe7yomZW6xWLPXNsM3hy7kdNxPgz762UodUkbFOKLyWQB8c2o6bO8g4/ Tables of Contents/all_files_ToC.htm
Process: file://C:\Program Files (x86)\Google\Chrome\Application\chrome.exe
Infection: Mal
You have to be a member of a particular group to access the file at that particular URL and the URL will likely change - Yahoo has been randomizing or dynamically encrypting that long middle part for a long time.
I suspect the latest avast update introduced some new rules in Network Shield that are being broken. It's unlikely that overnight Yahoo Groups has become unwittingly reprogrammed to incorporate something malicious in its files URLs.
Until this false detection is fixed, I have to turn Network Shield off in order to use the Files area of any Yahoo Group.
Tom