A phantom withdrawal is a cash withdrawal from an automatic teller machine where money has been withdrawn from an account, and neither the customer nor the bank admit liability.
If the banks are unable to find any error in their side, they conclude that the withdrawals were done by the customers. Many experts ascribe phantom withdrawals to the criminal activity done using the banking network itself. Ross Anderson, a leading cryptography researcher, has been involved in investigating many cases of phantom withdrawals, and has been responsible for detailing several weakness in the banking network.
References
Phantom withdrawal Wikipedia(Text) CC BY-SA