For anyone who has been getting fed up with the pointless annoying "Secure Folder Locked" notification you get everytime you restart your phone, I've just installed an app called "Autonotification" which you can use to block unwanted notifications. I would rather not have had to install such an app, and who knows if it has reduced the overall security of my phone, but as Samsung wouldn't give us the option of turning it off it seems worth it to put an end to this incredibly frustrating notification!
