App For Password Protecting messages


Afternoon folks not sure if posted in correct place but am looking for so me help. I have the HTC Desire HD Handset and its a great phone my proble i s i have a screen lock on it so when no one can access it when locked but my problem is once the screen is unlocked people can access my messages folder etc with it being a works phone i dont want people reading confidential text messages ettc , now is there an app which i could use to lock the messages once the phone is unlocked so no unauthorised access can be gained ??