Scam Shield can block Private callers by going to the Settings screen and selecting the Category Manager option where you will see an option to send “Private calls” to voicemail. By toggling this option to “on” you will send calls identified as Private to voicemail.

Scam shield defines a “Private” call as a call where the calling party has purposely chosen to obfuscate the number by using the *67 prefix when making the call.