This is a security feature, as Apple thinks most malware will be from developers that do not register at Apple. Since 2012,
Gatekeeper can check (new) apps by certificate. It recognises three levels: MAS (Mac App Store = reviewed by Apple), identified developers (registered at Apple for a certificate), and the rest (unknown developers). Initially (Lion) Gatekeeper was off (Allow from anywhere) by default. In Sierra, the “Allow from anywhere“ option is even hidden, to tighten security further and discourage unregistered developers. As Perian is from 2011, before developer certificates linked to Gatekeeper, it will be from an unknown source to Gatekeeper.
You can set your preference in System Preferences > Security & Privacy > General > Allow apps downloaded from ...
You can always manually override it, if needed, using the contextual menu. Right-click (or Control-click) on an app. Select Open. A slightly modified warning window will pop up, which now has [Open] and [Cancel] instead of [OK]. Click Open to override Gatekeeper. Gatekeeper will remember your consent, and won’t bother you again for this app.
