Hello,
I think Avast have fixed this issue, maybe in their latest virus definition updates. Problem was, if you already had the virus or whatever it was, the definitions couldn't update automatically because Avast itself was blocking the update when it detected the JS:Banker virus (falsely or otherwise). I basically just uninstalled Avast then downloaded the latest version & reinstalled. Everything appears to be normal again... at least so far!!
Geoff Pearson