Breach filing
ArchivedGroup Health Cooperative of South Central Wisconsin: 533,809 individuals, Apr 2024.
Group Health Cooperative of South Central Wisconsin reported a breach of unsecured protected health information to the HHS Office for Civil Rights on 8 April 2024. The filing records the organisation as a health plan in Wisconsin and lists 533,809 individuals affected, which makes it the 4th largest of the 126 Wisconsin filings on the register and the 39th largest of the 741 filings submitted nationally in 2024. Among the 10 Wisconsin filings made in 2024 it ranks 1st.
Individuals affected
533,809
As reported to HHS
Modelled cost (IBM 2025)
$85.4M
Upper bound, method shown
Rank in WI
4th
of 126 Wisconsin filings
Rank in 2024
39th
of 741 filings nationally
Section F.1 / The filing
As posted by HHS OCR
Every value below is the portal's own field for this filing, plus its rank within the register.
- Covered entity type
- Health Plan
- Individuals affected
- 533,809
- Breach submission date
- 8 April 2024
- Submission year
- 2024
- Type of breach
- Hacking/IT Incident
- Location of breached information
- Network Server
- Business associate present
- No
- State
- Wisconsin (WI)
- Portal status
- listed in the HHS OCR breach portal archive
- Rank in Wisconsin by size
- 4th of 126
- Rank in 2024 nationally
- 39th of 741
- Wisconsin median filing
- 3,657 individuals
- Register id (derived)
- WI-20240408-group-health-cooperative-of-south-centra
Section F.2 / In context
Where this filing sits in Wisconsin and in 2024
OCR classifies the incident as a hacking or IT incident, with the breached information held in a network server. Hacking/IT Incident is the type recorded on 83 of the 126 Wisconsin filings (66%) and on 83% of all filings submitted in 2024. Network Server appears on 40% of Wisconsin filings.
No business associate is recorded on the filing; 31% of Wisconsin filings do involve one. At 533,809 individuals the breach is 146 times the Wisconsin median filing of 3,657 and 133 times the national median of 4,000 across all 7,884 filings. It is one of 801 filings of 100,000 or more individuals.
As of 28 August 2026 the case is listed in the HHS OCR breach portal archive. OCR's closing summary of the case is reproduced in full below.
Wisconsin's breach notification statute (Wis. Stat. 134.98) requires notice to affected residents within 45 days after learning of the unauthorized acquisition. Its attorney general threshold: no AG notification requirement. The HIPAA Breach Notification Rule ran alongside it: notice to affected individuals and to HHS without unreasonable delay and no later than 60 days after discovery, which is the clock that put this filing on the portal.
Multiplying 533,809 individuals by IBM's $160 customer-PII cost per record (Cost of a Data Breach 2025, the figure the site's calculator uses) gives a modelled $85.4M; the 2026 edition's $192 gives $102M. Both are modelled estimates with the method shown, not costs disclosed by Group Health Cooperative of South Central Wisconsin. Because the filing is above the roughly 100,000-record range in which the per-record figure is reliable, the result is an upper bound, not an estimate: fixed costs are spread across far more records at this scale.
Section F.3 / OCR closing summary
The portal's archived description, in full
Written by the Office for Civil Rights when the case was closed and reproduced verbatim from the HHS export.
The covered entity (CE), Group Health Cooperative of South Central Wisconsin, reported that it was the subject of a ransomware attack that affected the protected health information (PHI) of 533,809 individuals. The PHI involved included names, Social Security numbers, addresses, dates of birth and medial record numbers. The CE notified HHS, the affected individuals, the media, and provided substitute notice. In response to the breach, the CE provided complimentary credit monitoring services to the affected individuals and implemented additional administrative, technical, and security safeguards. Staff were retrained on the requirement to protect and secure PHI.
Section F.5 / Modelled cost
533,809 individuals through IBM's per-record figures
Modelled cost / method shown, not a disclosed cost
Upper boundIBM 2025 customer PII, $160 per record
$85.4M
533,809 x $160
IBM 2026 customer PII, $192 per record
$102M
533,809 x $192
Method: individuals affected, as reported by Group Health Cooperative of South Central Wisconsin to HHS, multiplied by IBM's customer-PII cost per record (Cost of a Data Breach 2025 Figure 6 and the 2026 edition). No cost has been disclosed by the entity for this filing; the figure is a planning estimate, not a fact about the breach. IBM's per-record figures come from mid-volume breaches and IBM cautions against applying them to breaches involving millions of records; the site's per-record page explains where the multiplication holds and where it breaks down.
Context: IBM's average cost of a healthcare breach is $6.64M in the 2026 report ($7.42M in 2025); the global average across all sectors was $4.44M in 2025.
Cost per record: method and limits / Healthcare breach cost, IBM 2026
Section F.6 / Notification clock
Wisconsin statute and the HIPAA rule
State notification statute
Wisconsin: Wis. Stat. 134.98
- Notice to individuals
- Within 45 days after learning of the unauthorized acquisition
- Attorney general threshold
- No AG notification requirement
- Private right of action
- No: No PROA under the statute; failure to notify may support separate negligence claims
- Penalty
- Civil forfeitures up to $10,000 per violation, enforced by the AG and DATCP
The HIPAA Breach Notification Rule runs alongside the state statute: notice to affected individuals and to HHS without unreasonable delay and no later than 60 days after discovery.
Section F.7 / Peer filings
Wisconsin filings closest in size
Neighbours by size rank among Wisconsin filings in 2024, topped up from other years where 2024 has too few. Filings of 10,000 or more link to their own page.
| Covered entity | Type | Individuals | Submitted | Breach type | Location | BA |
|---|---|---|---|---|---|---|
| Advocate Aurora Health | Healthcare Provider | 3,000,000 | 14 Oct 2022 | |||
| Forefront Dermatology, S.C. | Healthcare Provider | 2,413,553 | 8 Jul 2021 | |||
| Adams County | Healthcare Provider | 258,120 | 11 Dec 2018 | |||
| University of Wisconsin Hospitals and Clinics Authority | Healthcare Provider | 85,902 | 5 Mar 2024 | |||
| Richland County, WI | Healthcare Provider | 76,365 | 9 Sep 2024 |
Index / Companion schedules
13 HHS breach register
→Hub: every filing, by state, year and entity.
04 Biggest breaches
→Mega-breaches with primary-source cost figures.
Industry / Healthcare
→IBM 2026: $6.64M average, 13 years at #1.
Regulation / HIPAA penalties
→OCR enforcement tiers and the 60-day rule.
11 50-state laws
→Deadline, AG threshold and penalties per state.
Cost / Per record
→Where the per-record model is reliable.
Provenance
Source: U.S. Department of Health and Human Services, Office for Civil Rights, Breach Portal (breaches affecting 500 or more individuals), retrieved 2026-08-28. Public domain. Individuals affected and dates as reported by the covered entity.
Portal: ocrportal.hhs.gov breach report. Statutory basis: HITECH Act section 13402(e)(4): the Secretary must post a list of breaches of unsecured protected health information affecting 500 or more individuals. Breaches affecting fewer than 500 individuals are reported to OCR annually and are not posted, so they are not on this register. Status wording follows the portal's two tabs ("Cases Currently Under Investigation" and "Archive") as of 28 August 2026; a filing moves to the archive when OCR closes the case. Modelled costs on this site are a method applied to the reported count, using IBM Cost of a Data Breach per-record figures, and are never a cost disclosed by the entity. This row: hhs-breach-archive__2026-08-28.csv, export row 1028.
Corrections: if you represent a listed entity and the portal row has been amended, email [email protected] with the portal entry and we will re-pull the export.