AirGap
Locks backup files disallowing malware (cryptolockers) to alter them
...\SYSTEM\CurrentControlSet\Services\AirGap\Parameters] key define folders where files you want to lock and include/exclude masks:
"Folder0001"="D:\\Backup\\Daily"
"Include0001"="*.vbk; *.vbi"
"Exclude0001"="*.tmp; *.temp"
And finally start AirGap service:
sc start AirGap
When you need to remove old (or update) backup files - stop AirGap service, remove files and start service again.