By Alina Selyukh WASHINGTON (Reuters) – U.S. companies that have fallen prey to hackers, exposing the private information of millions of customers, have often failed to take basic security precautions to protect client data, Illinois Attorney General Lisa Madigan told a U.S. Senate panel on Wednesday. Madigan said her office and that of Connecticut Attorney General George Jepsen are now leading a multistate investigation into recent data breaches that affected millions of customers of U.S. retailers Target Corp, Neiman Marcus Group LLC, and Michaels Stores Inc. On Tuesday, top executives of Target and Neiman Marcus told the Senate Judiciary Committee that hackers had found ways to penetrate their best security practices. Both companies bemoaned the sophistication of hackers behind recent data breaches that exposed the private data of millions of their customers.