Computer-implemented method and system are provided for verifying a financial instrument. The method comprises receiving identification of a source of funds; generating, using at least one processor, a series of verifying transactions involving the source of funds, transaction details of the series of verifying transactions varying from one transaction to another; storing the variable transaction details; initiating the series of verifying transactions; receiving provided transaction details from a user; comparing the variable transaction details with the provided transaction details; and selectively approving the use of the source of funds by the user, based on a result of the comparison of the variable transaction details with the provided transaction details.