Cornerstone Staffing Solutions Data Breach Investigation

Thousands of people who submitted a resume or worked through Cornerstone Staffing Solutions may now be dealing with the fallout of a serious cybersecurity incident. The Pleasanton-based staffing agency, which places workers in administrative, healthcare, IT, and light industrial roles throughout California and beyond, disclosed that a November 2025 cyberattack compromised personal information stored on its systems.

The company began notifying affected individuals and the California Attorney General's office, months after the intrusion reportedly took place.

According to public reporting, a ransomware group known as Qilin claimed responsibility for the attack and stated it pulled roughly 300 gigabytes of data from Cornerstone's network.

That haul reportedly included more than 120,000 resumes along with internal financial records, amounting to millions of individual data points tied to real people. The lawsuit alleges the exposed information included full names and Social Security numbers, the exact combination fraudsters need to file fake tax returns or take out loans in someone else's name.

Staffing agencies sit on a mountain of sensitive data because their entire business depends on collecting it. Job seekers hand over resumes, background check paperwork, and onboarding forms often without ever becoming a long term employee of the agency itself, which means many victims may not even remember giving Cornerstone their information in the first place. That makes this breach especially frustrating for people trying to figure out whether they are at risk.

If you applied for work through Cornerstone Staffing Solutions or were placed by the agency at any point, watch your mail closely for an official notification letter. Pull your credit reports, look for accounts or inquiries you do not recognize, and consider a credit freeze while the investigation continues. Save any letter or email you receive referencing this incident, since it may become important evidence later.

California law gives companies a legal duty to protect the personal information they collect, and when that duty is not met, the people whose data was exposed are the ones left cleaning up the mess.

The Lyon Firm has represented data breach victims across the country and understands how staffing and recruiting breaches like this one unfold. If your information was part of the Cornerstone Staffing breach, contact the data breach lawyers at The Lyon Firm today for a free, no obligation case review.