Indian Overseas Bank — online transaction successful without otp or pin

I tried to subscribe an app from play store and proceeded for the payment procedure... After giving the bank details i suddenly found that i have successfully subscribed the app without getting any otp or pin request... After some moment i also received the debited message from bank... This indicates that any one can easily do transaction by merely knowing my card number and cvv code.
I want the reason for this type of insecurity!!!??... And also some precaution advice!!