Today I checked Norton's site for dirtiest website. I decided to check how the Avast Web Shield worked and entered a chinese site which was reported with 243 risks. However, Avast Real Time shields could not detect any, so I downloaded a malicious image(.jpg) from that site, the file shield still could'nt detect it, but when I manually scanned it, a threat was detected. I thought that the file shield was not working, so I tested the eicar test file and a few other malware samples and it caught them! Later on I scanned with Malwarebytes and it found 12 infections in my registry! What's going on?