A device called a skimmer is installed in the card slot of the machine. When the card is inserted in the slot, this device captures the card details. A camera installed somewhere above the number pad, captures the ATM pin. These details are then used either to clone a card, which is used to withdraw money from ATMs, or the details are used to shop online.
If the ATM pad seem different from the usual, it is possible that the ATM machine has been tampered with. If the card reader seems loose or wobbly or protruding outward, tug it outward to see if there is an attachment that has been installed. Sometimes, a thin film is placed on the keypad to capture keystrokes. If you notice any such film, again avoid using that machine.
Another precaution that all bank customers should exercise is to enroll for their bank's SMS service so that they can receive real-time alerts in case of a fraudulent withdrawal from their account. Some banks have introduced a feature of ‘locking’ the card or setting limits on how much can be spent using the card.
Call the bank immediately and get your card blocked. This will prevent further withdrawals. Early notification will also help you get compensated if it is established that the breach did not occur due to your fault. The next step is to file a first information report (FIR) at a nearby police station.