If you are having debit card (ATM Card), you are exposed to risk of unauthorized withdrawal of money from your account without using PIN of debit card (ATM card).
Some of Indian bank’s Debit Card (like ICICI bank Visa debit card) may allow some known merchants to withdraw money from your account, if you provide DEBIT card (ATM Card) number, expiry date and CSC numbers (“Card Security Code”) [equivalent to CVV number of credit card] which is at back of ATM card, they may not need PIN of debit card or signature from you. In some cases they may also need not to use 3D security authorization for the payment.
Debit card is handled by Big MNC like Master Card, VISA etc, they may have some details of your bank account, they are also authorized to withdraw money from your account on your behalf and transfer it to any account worldwide.
In most of the cases they never try to make any unauthorized transaction from your account. But there is always scope of risk if you are using debit card (Even if you are not using internet banking).
So for the safety of your account, try to avoid discloser of your Debit card (ATM card), particularly ATM card Number and CSC number to any one online or offline as far as possible.
Use 3D security of your bank. ex- for SBI to make your account further protected.
the best way to protect your account is that keep most of the amount in Fixed Deposit, keep very less amount to the exposure of ATM card.