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Overview
In May 2025, Dentsu confirmed that hackers had accessed the systems of its UK division, Merkle, following a cyber attack discovered the previous month.
The breach potentially exposed the personal and financial information of current and former employees.
Dentsu’s investigation found that files containing bank and payroll details, salary information, National Insurance numbers and contact details had been taken from its systems.
Payroll and financial information is among the most sensitive data an employer holds. If it falls into the wrong hands, it could be used for identity theft, fraud or other financial crime.
While Dentsu’s investigation initially focused on employee information, reports have suggested that some client and customer data may also have been affected. This includes a possible link to the cyber incident involving train operator LNER, whose customer communications supplier is believed to be linked to Merkle.
This has not yet been confirmed.
If it’s confirmed that Dentsu failed to adequately protect employee data or customer data, those affected could be entitled to compensation under UK data protection law.
We are monitoring the situation closely. Register your interest today, and we will keep you updated if one of our regulated UK partner law firms is able to take this claim forward.
Dentsu data breach – At a glance
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Staying informed is the first step towards change. By registering alongside others affected, you’re showing that people expect better. And that when something goes wrong, they want to see it put right.
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Latest updates on the Dentsu data breach
July 2026
There have been no significant public developments since Dentsu disclosed the breach.
November 2025
Dentsu issues a public statement confirming the nature and scope of the data exposed, stating that files taken from its Merkle network included payroll, bank, and contact details of current and former UK employees.
October 2025
The data breach is first reported by the press.
We’ll provide more updates on the data breach claim as they occur.
Are you affected by the Dentsu data breach?
Register to stay updated and we’ll let you know if a partner law firm takes this claim forward.
Frequently asked questions about the Dentsu data breach
Yes. Dentsu has confirmed a data security incident affecting its UK operations through its marketing division, Merkle. The company detected unusual activity on its servers and has since contained the breach, launched an investigation, and notified the ICO, NCSC and law enforcement.
The breach primarily involves current and former employees of Dentsu’s UK operations, including its marketing division Merkle.
However, independent media reports suggest that some client and customer data may also have been affected.
The company has contacted those whose data may have been compromised and is offering a free 12-month membership to Experian Identity Plus, which provides credit and dark-web monitoring.
If it’s confirmed that Dentsu failed to protect employee and/or customer data in line with UK data protection law, those affected could be eligible for compensation. Join the Claim will continue to monitor the situation and update affected individuals as more details emerge.
We are not a law firm. Our role is to keep people informed about potential group actions if one of our regulated UK partner law firms is able to take this claim forward.
By registering, you’ll stay up to date with any developments — from investigations to possible legal action.
No. Registering simply means you’ll receive updates. If a law firm later takes on the case, you’ll be given the option to learn more about the process and any potential costs before deciding whether to take part.
A group action claim allows people affected by the same issue to take action together. This strength in numbers helps stand up to big organisations. Join the Claim helps connect people with law firms so these actions have a real impact.
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When you register your interest with Join the Claim, we’ll keep you updated if one of our regulated partner law firms decides to take the claim forward. However, other law firms may also investigate or pursue claims independently of Join the Claim.
Registering for updates does not prevent you from speaking to another law firm or joining a claim elsewhere.
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