In order to protect the privacy, you can lock folder that saved important files. (in version 3.9.0+)

1. Tap the three-point in the right low of folder or long-press the folder.

2. choose "Set Password" 

After you unlock folder to read, the lock is opened until you close GalleryVault. In the meantime, you lock folder again by tap three-point or long-pressing folder.