when you report it, avast will fix the detection.....if it is wrong.
if correct, then avast saved your comp
avast is usually correct in these detections and often the first one to detect website infections
no website is 100% secure, the bad guys fish in the pond that has most fish, so if this is a site with many users then it is of course of interest to hack
report it and see if avast reply here..... OBS and dont expect a reply after 5 minutes.