Acxiom , one of the world's largest specialists in customer and information management, confirmed Friday that it had been hacked, and that information about some customers of its clients was downloaded.

"An individual, who was a former employee of an Acxiom client, was arrested in conjunction with this incident," the company said in a statement Friday. "According to law enforcement, the individual arrested was a known sophisticated hacker. He evidentially gained access through hacking of encrypted passwords."

The Little Rock, Ark.-based firm said the stolen information was retrieved. "Law enforcement has notified Acxiom that they do not believe that any of the data has been released to other parties or used for fraudulent purposes," the company said.

The breach involved one external FTP server outside Acxiom's firewall that is used to transfer files back and forth between Acxiom and its clients. The company said no internal databases were accessed and no breach penetrated its firewall. Additionally, the firm said only a small percentage of its clients' data was involved in the incident.

Acxiom's client list includes a number of Fortune 500 companies, like Microsoft, IBM, AT&T, and Blockbuster. The company says it services 14 of the top 15 credit card companies, 7 of the top 10 auto makers, 7 of the top 10 media entertainment companies, 6 of the top 10 magazine publishing companies, 4 of the top 5 telecom companies, 5 of the top 6 retail banks and 3 of the top 5 retailers.

Acxiom, which prides itself as a leader on consumer privacy issues, said this is the first such incident that it ha experienced, adding that it immediately changed all passwords to the FTP server involved. The company said it is in the process of communicating with all clients potentially affected by the breach.

"Acxiom is proud of its longstanding commitment to the security of our systems and our efforts toward continuous improvements in that area, so we deeply regret this breach," Acxiom Company Leader Charles D. Morgan said in a statement. "In recent years, Acxiom has conducted extensive internal security audits, and we have been subject to multiple external audits performed by clients, vendors and others. Our already high standards will be set even higher, and we have begun a comprehensive review of our systems and procedures, with the help of nationally renowned security experts, to guard against similar incidents in the future."