Express Scripts said Thursday it has received a letter demanding money from the company under the threat of exposing records of millions of patients.
The threat was made in an anonymous letter that the company turned over to federal investigators. The letter, received in early October, included personal information on 75 people covered by Express Scripts, including birth dates, social security numbers and prescription information.
The company said it has alerted customers and is investigating the potential security breach.
"We are cooperating with the FBI and are committed to doing what we can to protect our members' personal information and to track down the person or persons," company Chief Executive George Paz said.
Express manages prescription benefits for more than 50 million people through thousands of clients, including health insurers, employers and union-sponsored plans.
Express staff said in a statement online they believe they have identified the area where the data was stored and "have instituted enhanced controls."
Company shares fell $3.72, or 6%, to $58.05 in afternoon trading.