Looking for extra security in the stock Messages app? The jailbreak tweak ConvoProtect can be used to lock and hide conversation threads. The package adds this functionality to iOS and even works with third party apps WhatsApp and Kik.
Once installed, texts and iMessages can be secured by selecting the contacts or groups involved in the threads to be locked. Entering a passcode will lock the conversation. After a conversation is locked, accessing its contents will require entering the passcode.
For extra security, message threads can be hidden entirely. New messages in these hidden conversations are still delivered as notifications, but the conversation will not appear in the Messages app unless the Hidden toggle is switched off.
Message previews can be hidden as well. An Activator gesture can be configured to toggle hidden messages, which makes it convenient to show hidden message threads temporarily. ConvoProtect will even protect its own settings with a master password for better security.
ConvoProtect is available on Cydia from the BigBoss repo for $1.99. Jailbreaking iOS 7.1.x is now possible with Pangu. Check here for instructions on how to jailbreak iOS 7.0.x with evasi0n 7. You can also find out how to purchase and install Cydia tweaks with this guide.