BreachCensus

Quest Diagnostics

United States of America

Quest Diagnostics is an organisation in California. It appears on the Massachusetts Attorney General breach-notification register and the California Attorney General breach-notification register with 4 confirmed incidents (5 filings); the most recent notice was filed on April 5, 2023.

Data as of October 23, 2026.

Sources

Confirmed incident

US-MA

Disclosed
April 5, 2023

Timeline

  1. April 5, 2023
    Reported to regulator Regulator

    MA AG breach notification: 4 Massachusetts residents affected

    source
  2. October 21, 2026
    Press coverage Press

    press report (acknowledged): the unauthorized access was first identified on October 21, 2026

    source
  3. October 22, 2026
    Press coverage Press

    press report (press_reported): In its October 22, 2026, Form 8-K filing, the company said the unauthorized access was first identified on October 21, 2026

    source
  4. October 22, 2026
    Press coverage Press

    press report (acknowledged): A key system used by Quest Diagnostics to manage medical test results was taken offline on Thursday after the company discovered unauthorized access.

    source
  5. Undated
    Press coverage Press

    press report (acknowledged): Quest Diagnostics said it learned of a cyber breach of one of its systems this week

    source
  6. Undated
    Press coverage Press

    press report (individuals_notified): The company said it discovered the hack on Wednesday and notified federal law enforcement

    source

Litigation

  • Possible litigation — multiple candidate dockets found, not yet resolved to a single case.
What a Massachusetts notice means

Governed by M.G.L. c. 93H. Notice to the Attorney General is required for a breach affecting any number of Massachusetts residents' personal information -- the statute sets no minimum count.

Note: the count is Massachusetts residents only, not a total.

Massachusetts breach-notification register ↗

Confirmed incident

Filed in CA and MA

The same incident was filed separately with 2 jurisdictions within a few days of each other (CA and MA) — shown here as one incident.

Occurred
October 29, 2021
Disclosed
November 16, 2021

Timeline

  1. November 16, 2021
    Reported to regulator Regulator

    CA AG breach notification: an unknown number of California residents affected

    source
  2. November 16, 2021
    Reported to regulator Regulator

    MA AG breach notification: 156 Massachusetts residents affected

    source

Litigation

  • Possible litigation — multiple candidate dockets found, not yet resolved to a single case.
  • Possible litigation — multiple candidate dockets found, not yet resolved to a single case.
What a California notice means

Governed by Cal. Civ. Code §1798.82. A copy of the notification must be sent to the Attorney General when a single breach requires notifying more than 500 California residents.

Note: no affected-count is published on this register.

California breach-notification register ↗

Confirmed incident

US-CA

Occurred
November 26, 2016
Disclosed
December 12, 2016

Timeline

  1. December 12, 2016
    Reported to regulator Regulator

    CA AG breach notification: an unknown number of California residents affected

    source
  2. February 13, 2017
    Litigation filed Court

    RECAP docket 2:17-cv-00948 (njd): MORROW v. QUEST DIAGNOSTICS INCORPORATED

    source

Litigation

Confirmed incident

US-CA

Occurred
November 17, 2014
Disclosed
December 19, 2014

Timeline

  1. December 19, 2014
    Reported to regulator Regulator

    CA AG breach notification: an unknown number of California residents affected

    source

Related

Disclosed around the same time