Greylock McKinnon Associates (GMA), a private litigation-support firm, reported a cyber incident affecting information it held for clients, including the U.S. Department of Justice. One Maine Attorney General filing lists 341,650 affected people. But describing the incident as 340,000 standalone Social Security numbers exposed is imprecise: for the DOJ-related group, the notice says Social Security numbers were included within Medicare Health Insurance Claim Numbers, and that an SSN by itself was not affected. The notice also says Medicare benefits and coverage were not affected.
What happened at Greylock McKinnon Associates?
GMA provides economic analysis and litigation-support services to legal, business and government clients. For the DOJ-related population, the firm said it held the information while supporting the department in a civil litigation matter. The official notice describes unusual activity on GMA’s internal network; it does not say that the DOJ’s own systems were breached. GMA’s DOJ-related notification says the affected people were not subjects of the investigation or related litigation.
The Maine Attorney General’s filing characterizes the event as an external-system breach or hacking incident. It reports 341,650 affected people in that filing. The notice says information may have been affected; it does not establish that every listed item was downloaded, published or misused.
Incident timeline
- May 30, 2023: The Maine filing lists this as the breach date. GMA said it detected unusual activity on its internal network.
- February 7, 2024: The filing lists this as the discovery date. GMA said it confirmed affected identities and contact information.
- April 5, 2024: The filing lists this as the date consumer notifications were sent. The DOJ-related notice is dated April 8, 2024.
These dates and the affected count appear in the Maine Attorney General’s 341,650-person filing and the individual DOJ-related notice.
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What information may have been involved?
The DOJ-related group
For the group described in the DOJ-related notice, potentially affected information included names, dates of birth, addresses, Medicare Health Insurance Claim Numbers, and some medical or health-insurance information. The filing explains an important distinction: the SSN was contained within a Medicare claim number for this population; it was not an SSN exposed by itself. That is why the shorthand “340,000 Social Security numbers” overstates what the official notice establishes.
A Medicare Health Insurance Claim Number is an identifier used in connection with Medicare. The notice’s qualification concerns the form in which the SSN appeared in this group’s data; it does not mean the exposed information was harmless or that the number should be treated as a standalone SSN.
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Other GMA notices
GMA filed notices for other populations whose information differed. Some notices identify a name and SSN; other categories described across the separate notices include financial-account information and an IRS e-file PIN. Those categories should not be assumed to apply to the DOJ-related group or to every person notified. See the Maine filing for another GMA population, the Massachusetts notice for a 5,465-person population, and the Massachusetts notice for another GMA population.
Why do published affected-person counts differ?
The figures refer to different regulatory notices and litigation-defined groups, not necessarily competing estimates of one identical population. In particular, the settlement’s class sizes should not be substituted for the 341,650 people in the Maine filing.
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| Population or filing | People | What the figure describes |
|---|---|---|
| DOJ-related Maine filing | 341,650 | One breach-notice population; the DOJ-related notice describes Medicare claim numbers containing SSNs, among other potentially affected information. |
| Separate Maine filing | 5,465 | A different notice population; the filing identifies names and SSNs. |
| Another Maine filing | 13,549 | A separate affected population with different notice details. |
| Settlement damages class | 20,819 | People whose SSNs were affected under the settlement’s class definition. |
| Settlement injunctive-relief class | 998,923 | A broader litigation-defined group whose personal information was affected. |
The settlement counts come from legal class definitions, while the Maine counts come from separate breach filings. Differences in scope and definitions explain why they should not be added together or treated as a single final tally.
Did the incident affect Medicare benefits or mean people were under investigation?
No, according to GMA’s DOJ-related notice. It says notified people were not subjects of the DOJ investigation or associated litigation, and that current Medicare benefits and coverage were not affected. That assurance addresses benefits and coverage; it does not erase the potential identity risk associated with personal or Medicare-related identifiers.
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What did GMA say it did in response?
In the DOJ-related notice, GMA said it took steps to mitigate the incident, consulted third-party cybersecurity specialists, notified law enforcement and the DOJ, and deleted DOJ data from its systems after the incident. It also said affected people were offered credit monitoring or identity-protection support. These are statements in the company’s notice.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should someone who received a notice do?
- Read the notice that was sent to you. The letter identifies the affected population and information relevant to you. Do not infer that another GMA group’s data categories or service offer apply to your case.
- Enroll in the free service offered to you, if eligible. The 341,650-person Maine filing lists 24 months of Cyberscout identity-theft protection and credit monitoring. A separate GMA notice lists 12 months of Experian IdentityWorks. Follow the instructions and deadline in your own letter; do not assume a different population’s offer applies. The offers are described in the 341,650-person filing and the separate 5,465-person filing.
- Consider placing a credit freeze. Contact each of the three nationwide credit bureaus through its official website or contact channel. A freeze restricts access to your credit file for many new-credit applications; monitoring instead alerts you to activity. Neither makes existing accounts immune to fraud.
- Review credit reports and financial accounts. Look for unfamiliar accounts, inquiries, addresses, collections or transactions. Keep the breach letter and confirmation of any monitoring enrollment in a safe place.
- Be cautious about unsolicited contact. Do not give callers or email senders your passwords, one-time codes or payment information because they claim to represent GMA, DOJ, Medicare or a monitoring provider. Use contact details in your notice or on the official settlement site, rather than links or phone numbers in an unexpected message.
- Act promptly if you spot fraud. Contact the relevant creditor, bank or insurer using a verified contact channel. You can report identity theft to the Federal Trade Commission and local law enforcement, and keep copies of reports and correspondence.
What is the class-action settlement, and what can people still do?
The case is In re Greylock McKinnon Associates Data Security Litigation, Case No. 1:24-CV-10797-DJC, in the U.S. District Court for the District of Massachusetts. The settlement materials say GMA denies wrongdoing and liability; the settlement is not a court finding that GMA violated the law. The settlement FAQ and settlement agreement define two groups:
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- Damages Settlement Class: U.S. residents whose Social Security number was affected.
- Injunctive Relief Settlement Class: U.S. residents whose personal information was affected.
Under the agreement, the damages class could seek reimbursement of documented losses up to $10,000 per person, a possible pro-rata cash payment and one year of single-bureau credit monitoring, subject to the settlement’s terms, claim requirements and available funds. The broader injunctive-relief class may receive security-practice changes rather than cash. Eligibility for the broader group does not by itself establish eligibility for damages.
The settlement FAQ states that the deadline to object passed on June 9, 2025. That date is not a current claim-filing instruction, and the materials cited here do not establish whether any claim process remains open in October 2026. Check the official settlement site for current administrator information and deadlines before taking action. People with an existing lawsuit should consult their lawyer before making decisions; class membership and the settlement’s release may affect legal rights.
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