A group of New York residents whose health data were compromised during a data hack are suing the state's largest health insurance providers alleging negligence.

Matthew Fero, Shirley Krenzer and Erin O’Brien, individually and on behalf of others affected, filed a class action lawsuit on Sept. 18 in the U.S. District Court for the Western District of New York against Excellus Health Plan and Lifetime Healthcare, according to an article published by LegalNewsline.com.

Hackers gained access to the defendants' data systems around December 2013 and operated undetected for the next 20 months.

The defendants allegedly discovered the hack Aug. 5 but the plaintiffs say it took until Sept. 9 for the insurers to disclose the breach to the public. Excellus also has yet to disclose which clients were affected.

The plaintiffs are suing for negligence in safeguarding personal data and acting accordingly. They seek a jury trial and an undisclosed amount for damages made during the data breach, court costs and an injunction forcing the defendants to disclose who was affected by the breach immediately.

On its website, Excellus President and CEO Christopher C. Booth offered details about the breach and the organization's actions since. "We worked closely with Mandiant, one of the world’s leading cybersecurity firms, to conduct our investigation and to remediate the issues created by the attack on our IT systems. We are taking additional actions to strengthen and enhance the security of our IT systems moving forward."