Dentsu, a major advertising and PR firm based in Japan, has revealed a data breach involving its subsidiary, Merkle. The breach affects clients, suppliers, and employees, as hackers accessed sensitive files from Merkle's network. Dentsu detected unusual activity and took precautionary measures, including shutting down some systems. The breach affects personal information, such as contact details, salaries, bank data, and National Insurance numbers. Affected individuals are being notified and offered free dark web monitoring. While Dentsu's Japan operations remain unaffected, the company anticipates some financial repercussions from the breach, though the extent is still being evaluated. There's uncertainty about whether this incident is linked to a ransomware attack, and no group has claimed responsibility so far. Dentsu has indicated it is unaware of any public sharing of the stolen data but has mentioned taking steps to prevent such disclosure, which raises questions about potential ransom negotiations. The company has engaged third-party cyber incident response firms and notified law enforcement as part of its investigative measures.