Calculator is the Vault app can secretly Hide Pictures, Hide Videos and Lock Apps without anyone knowing as gallery lock installed in your phone looks as just a regular calculator. Your files will be secretly stored in vault and can only be viewed after a Numeric PIN is entered on calculator panel of this app. The app is cleverly disguised as "Calculator" in the App Drawer.
The security report shows that this application is safe. Mallow is the official developer of the app that can be found in the Productivity category. Calculator Vault has been downloaded and installed by over 1M users and the most recent release is dated Dec 26, 2018.