Names and places mentioned herein are hypothetical.

When Tom went to withdraw money from an ATM machine he could only see the below message,

Sorry
You have insufficient funds available

This was unbelievable to him and he checked with the bank and heard that the money was withdrawn twice from the last ATM he withdrew, whereas he was pretty sure that he withdrew only once from that place.

Then he phoned one of his friends and explained what happened. The friend who was aware of forensic issues to a certain extent made him educated of fixing skimming devices on top bars, card slots and pin pads of ATMs with cameras to get the card details and pin numbers, which enable the skimmer to forge the cards and withdraw money.

Precaution tips: Use the ATM machines that are located in branches.
Shake the card slot and pin pad to check whether it is a skimming device (removable).
Cover the keypad with your other hand while typing your pin code.