FolderLock is a new tweak available in Cydia that allows you to password protect / lock folders on iPhone, iPad and iPod Touch running iOS 4.0 or higher.
There are numerous reasons why you would want to password protect/lock folders, whether it be adult content or other personal data (Email App, Messages, Contacts, Call history, browser history, etc.).
Protect your folders with password. You can set a password via Settings.app for your folders. You can also Enable/Disable this tweak, and protect some of iOS functions like Spotlight and Multitasking.
Obviously you can lock Settings.app, so nobody can change your password. Set password confirmation via Settings.app
FolderLock does not create a new icon on your homescreen. You can enable/disable FolderLock password protection from Settings.app.
You can purchase and download FolderLock from the Cydia Store for $1.99. Since it requires your iPhone, iPad or iPod Touch to be jailbroken, you can find jailbreak guides in Jailbreak iPhone/iPod Touch and Jailbreak iPad categories.
FolderLock in Action