Thru scan the files up to 250MB, files with larger size are passed w/o scanning for performance purposes.
Scanning limits can be changed per environment.
Until scanning is completed, files are not transferred and are not available for download.
By default this setting is enabled : Deny download of the files until scanned by Antivirus
Administrators do have the ability to globally disable the blocking that is in place until the file has completed being antivirus scanned.
Disabling the blocking means the file will be available instantly for download but may have not been scanned yet.