Cornerstone Staffing Solutions says a November 2025 network intrusion may have exposed Social Security numbers and other sensitive data, with a ransomware group claiming responsibility.
Cornerstone Staffing Solutions, a California-based staffing and recruiting firm, disclosed a data breach that occurred in November 2025, notifying at least 4,425 Texas residents and 243 Massachusetts residents that their personal information may have been exposed.
Cornerstone said an unauthorized actor may have accessed certain systems within its network between Nov. 6 and Nov. 21, 2025, and that there were signs some data may have been removed from the environment, though the specific files involved could not be determined with certainty. The company said it became aware of suspicious activity on its network on or around Nov. 17, 2025, and launched a forensic investigation.
Dark web monitoring found that the ransomware group Qilin appeared to claim responsibility for the attack, posting on the Tor network on Nov. 13, 2025 that it had obtained data from Cornerstone.
The personal information that may have been exposed includes names, addresses, Social Security numbers, driver’s license numbers, other government-issued identification numbers such as passport or state ID numbers, financial account and card information, medical information, health insurance information and dates of birth. Cornerstone said the breach was disclosed to the California attorney general’s office and that it began notifying affected individuals by U.S. mail on Sept. 11, 2026.
The company said its notification letters explained how affected individuals can place fraud alerts with the three major credit reporting bureaus and request a security freeze, which prevents the bureaus from releasing information from a consumer’s credit report without authorization, and included contact information for Equifax, Experian and TransUnion.
Murphy Law Firm said it is investigating potential legal claims on behalf of individuals whose information was compromised in the breach and is evaluating a possible class action lawsuit. The firm said the exposed information could be used by cybercriminals for identity theft or fraud, or posted on the dark web.
Smith Temporaries Inc. dba CornerStone Staffing, is a separate business and is not affiliated with Cornerstone Staffing Solutions Inc.
