download from trusted forums: LinuxSat-Support, OpenATV, Vu-Community, or TK (TechKings) . Look for backups with posted MD5 checksums and positive user comments.
While you can create your own backup, many users start with a base image from a trusted team: VTi (Vu+ Team Image) vu solo 4k backup images
Focuses on performance and simplicity; however, note that official active support for Vu+ hardware has been reduced recently. download from trusted forums: LinuxSat-Support