Unauthorized login protection is a set of measures taken to enhance the security of online services and systems. Unauthorized logins include cases where login credentials (IDs, passwords, etc.) exploited by phishing attacks and targeted attacks are used, and cases where logins are attempted by brute-force entering IDs/passwords (dictionary attacks). Such unauthorized access not only leads to the leakage of personal and confidential information, but may also lead to financial damage and loss of credibility of the company, such as fraudulent accounting and obstruction of EC sites. Therefore, countermeasures against unauthorized logins are very important and are carried out as part of security enhancement. Specific measures include increasing the strength of login credentials, introducing multi-factor authentication, and introducing systems to detect suspicious logins (e.g., exploitation of leaked information, identification of malicious tool communications).