Default [Q] type password to decrypt data storage

Hello there, I had this problem before I used CWM and custom ROMs, it happened when i am using the stock ROM 11.A.0.1.8 Rooted and using the app WifiKill. I enabled Wifikill then after I click the Disable button the phone rebooted then this message shows up : "type password to decrypt data storage" along with a Xperia Chinese Keyboard, Xperia Tipo Dual St21i2, anybody had the same experience? and how that happened even though I did't encrypt the storage, and now I am using the vegeance and stock 11.a.0.6.8, how can I encrypt my phone data storage? thanks