Passwords are essential to enhance security in the information system fields, but many vulnerabilities found that passwords can be stolen while being entered. Attackers are especially interested in bank account passwords and personal identification numbers (PINs). Thus, we aim to investigate the possibility of identifying the digit passwords stored in the brain from a neuroscientific perspective. To achieve this goal, we observed hemodynamic responses while viewing 6-digit random numbers (Task 1) and a preset virtual 6-digit password (Task 2), using functional near-infrared spectroscopy (fNIRS), the latest neuroimaging technique. As a result, we found the signal differences between Task 1 and Task 2, indicating that Task 2 has relatively low brain activity compared to Task 1. We found also a gender difference in brain activity, which requires gender-specific security measures. Therefore, our results suggest that attackers or third-party groups can identify the 6digit passwords stored within the brain. We provide the possibility of neuro-crimes using fNIRS for the first time.