Boot virus detected on partial disk image, false positive?

[1234ava]

Avast Free detected WXY-B boot virus on a Macrium Reflect image file of mine. I suspect a false positive though.
I gather WXY-B infects the mbr and the 1st partition boot sector, but there was no 1st partition in my image. It wasn't a full disk image: it had just the disk's mbr and two final partitions, including an unformatted partition. See screenshot below, the imaged partitions are on the far right hand side.


Besides, other Reflect images I created on the very same day, containing the same disk mbr but some other partitions on it, were NOT detected as infected with WXY-B.

[Pondus]

have you tested file at www.virustotal.com  ? .... if tested before, click rescan for a fresh result
post link to scan result here

[1234ava]

It's a disk image file sized over 1 GB, so I cannot upload it to VirusTotal.

[Pondus]

report it here  https://support.avast.com -> avast virus lab   and you will get instructions how to send it to the lab so they can check it

[1234ava]

Done, thanks!

[1234ava]

Avast Virus team examined my disk image file and confirmed it is safe, no boot virus, just like I thought.