Mid Michigan Medical Billing Service, Inc.: 28,185 individuals, Jan 2026.

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 148 of the 238 Michigan filings (62%) and on 86% of all filings submitted in 2026. Network Server appears on 45% of Michigan filings.

A business associate is recorded as present on the filing, as it is on 30% of Michigan filings. At 28,185 individuals the breach is 7.5 times the Michigan median filing of 3,754 and 7.0 times the national median of 4,000 across all 7,884 filings. It sits in the 10,000 to 99,999 band, which holds 1,938 filings.

As of 28 August 2026 the case is listed by HHS OCR under Cases Currently Under Investigation. OCR has not published a closing summary, so this page is limited to the fields on the filing itself; the archive entry that follows a closed investigation usually adds a short account of what was exposed and what the entity did afterwards.

Michigan's breach notification statute (MCL 445.72) requires notice to affected residents without unreasonable delay. Its attorney general threshold: not currently required (pending SB 360 would require it at 100+ residents). 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 28,185 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 $4.51M; the 2026 edition's $192 gives $5.41M. Both are modelled estimates with the method shown, not costs disclosed by Mid Michigan Medical Billing Service, Inc.. For scale, IBM's 2026 average cost of a healthcare breach is $6.64M, so this filing models at 0.8 times the sector average.