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A recent data beach could have exposed resident, customer, and service user data across three London councils. Has your information been compromised?

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Global marketing giant Dentsu has confirmed a data breach affecting the systems of its UK division Merkle, potentially exposing the personal and financial details of current and former employees.

Early findings show that files containing bank and payroll details, salary information, National Insurance numbers, and contact details were taken from Dentsu’s servers. The company says there’s no evidence so far that this data has been published online.

However, payroll and financial data is among the most sensitive information a company holds, and if it falls into the wrong hands, the consequences can be devastating, leading to identity theft, fraud, or long-term financial harm.

While Dentsu’s investigation initially focused on employee information, new reports suggest that some client and customer data may also have been affected. This includes the recent breach at train operator LNER, whose customer communications supplier is believed to be linked to Merkle.

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.

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Dentsu data breach – At a glance

Status Stay Informed
Data stolen
Bank, payroll information, personal data and more
Latest update
September 2025

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Join the Claim is bringing people together — uniting those who want answers, accountability and stronger data protections from the companies they trust.

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.

What do we know about the Dentsu data breach?

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  1. The company says it detected unusual activity on Merkle’s network. Cybersecurity specialists were brought in to investigate, and the breach has been reported to the relevant authorities.
  2. Affected employees are being contacted directly and offered a free one-year membership to Experian Identity Plus, a service that monitors for identity theft and dark-web activity.
  3. Independent reports suggest that some client and customer data may also have been affected, potentially including LNER customers. However, this has not yet been confirmed by the company.

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Latest updates on the Dentsu data breach

  • September 2025

    Dentsu issues a public statement confirming the nature and scope of the data exposed,statingthat files taken from its Merkle network included payroll, bank, and contact details of current and former UK employees. Around the same time, reportsemergedlinking the breach to a separate incident involving LNER’s customer communications supplier, which is understood tooperatewithin Dentsu’s Merkle network.

  • June 2025

    The data breach is first reported by the press.

We’ll provide more updates on the data breach claim as they occur.

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Are you affected by the Dentsu data breach?

Dentsu is contacting all affected employees and former employees to let them know. Customers of other companies may also be affected. Register to stay updated and we’ll let you know if a partner law firm takes this claim forward.

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Frequently asked questions about the Dentsu data breach

If you win your claim, a percentage of your compensation (agreed in advance) will be deducted as a success fee to cover legal costs. All terms are clearly explained before joining. You can find out more in our handy guide.

Compensation can come in two ways: through a settlement, where the defendant agrees to pay without going to trial, or through damages, which are awarded by the court if the case is won. Compensation is designed to reimburse you for the harm or loss you’ve experienced – whether that’s financial, emotional, or related to your rights as a consumer or employee. Compensation amounts vary depending on the nature of the claim, how many people are involved, and how badly individuals were affected.


The duration of a claim depends on its complexity and the legal process involved. Your solicitor will keep you updated every step of the way.

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JoinTheClaim.com is a platform that helps individuals and businesses find and join group legal actions. We do not run the group actions ourselves. Instead, we help connect eligible claimants with regulated UK law firms.

Yes, both individuals and businesses may be eligible to join group claims, depending on the specific case.

Eligibility varies by claim. Where we have a partner firm in place, you can use our quick online checker to determine if you meet the criteria for the specific group action.

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