Cohen Milstein is recognized as one of the leading data breach plaintiff law firms in the United States, having played a leadership role in virtually every major data breach class action litigated to date. In addition to spearheading cutting-edge litigation strategy, we are highly regarded by co-counsel and the judiciary alike for our collaborative efforts in pre-litigation investigations, working with top data privacy and economic experts, our ability to deftly handle complex discovery for large-scale data breach class actions, ensuring streamlined, efficiencies of scale, as well as our exceptional motion practice work.

We welcome co-counsel opportunities with other consumer protection law firms, nationwide.


We have the unique honor of being court-appointed as Lead, Co-Lead Counsel or serving as Steering Committee Counsel in numerous major data breach class action litigation in the United States. Our Data Breach & Cybersecurity Litigation team is led by:

  • Douglas J. McNamara – President of the American Association for Justice Class Action Litigation Group, Mr. McNamara specializes in litigating complex, nationwide and multi-state class action lawsuits. Mr. McNamara is also highly regarded for his thought leadership on such topics as federal preemption, class certification, and class action damage models, and is frequently appointed to class and MDL Plaintiffs’ Steering Committees and/or Expert Committees.

Members of our Data Breach & Cybersecurity Litigation team also include the former Deputy Associate Attorney General of the U.S. Department of Justice and former cybersecurity defense attorneys.

Relevant national rankings include:

Representative Matters – Current Cases

  • In re: Marriott International Inc. Customer Data Security Breach Litigation (D. Md) –On February 21, 2020, the court largely denied Defendants’ motion to dismiss, allowing Plaintiffs claims to move forward in this data breach class action, which alleges that, by the Marriott’s own admission in November 2018, a data breach compromised the personal information of nearly 400 million customers who made reservations at Starwood-branded hotels., This constitutes one of the largest data breaches in U.S. history. In April 2019, Cohen Milstein’s Andrew N. Friedman was court appointed Consumer Plaintiffs’ Co-Lead Counsel to oversee the litigation.
  • In re MGM Resorts International Data Breach Litigation (D. Nev.) – On February 1, 2021, the court appointed Cohen Milstein’s Douglas J. McNamara as Co-Lead Interim Class Counsel in this consolidated data breach class action against MGM Resorts related to the July 2019 data breach of personal information of between 10.6 million and 142 million MGM resort guests and customers.
  • In Re: Blackbaud, Inc., Customer Data Breach Litigation (D.S.C.) – Cohen Milstein is representing plaintiffs in a putative data breach class action against Blackbaud, a cloud computing account management and billing services company for its failure to protect the personal information of its client customers, including hospital patient record information and social security numbers, during a data breach that started in February 2020. On February 16, 2021, Cohen Milstein’s Douglas J. McNamara was court-appointed to the Plaintiffs’ Steering Committee.