The obligation to identify yourself – your bank has to know you!
Banks are required to know their customers. This consists both of knowing the identity of their customer (identification requirement) as well as to have a knowledge about their normal pattern of transactions, such a transfers, amounts paid into their accounts as well as their business connections.
Banks require this information as they are obliged to prevent money laundering and terrorist financing. If the bank spots a transaction that appears to be abnormal, then the bank is obliged to follow up this transaction.