Method, device, and system of detecting a mule bank account, or a bank account used for terror funding or money laundering. A method includes: monitoring interactions of a user with a computing device during online access with a bank account; and based on the monitoring, determining that the bank account is utilized as a mule bank account to illegally receive and transfer money, or is used for money laundering or terror funding. The method takes into account one or more indicators, such as, utilization of a remote access channel, utilization of a virtual machine or a proxy server, unique behavior across multiple different accounts, temporal correlation among operations, detection of a set of operations that follow a pre-defined mule account playbook, detection of multiple incoming fund transfers from multiple countries that are followed by a single outgoing fund transfer to a different country, and other indicators.