Difference between on-demand and automatic scanning?


Is there a difference between on-demand and automatic scanning in Bitdefender Free?


For example, if you download a file from the internet, doesn't Bitdefender Free scan it as soon as it is written to the drive?  Is there any reason to then drag-and-drop the file onto Bitdefender Free to have it manually scanned?


Also, when does the automatic scanning of files take place?  On read?  On write?  On execute?  All three?