More than 6,500 CNET Networks employees and relatives are being notified of a possible data breach after burglars stole computer systems from the offices of the company that administers the Internet publisher's benefit plans.

CNET was one of several clients affected when burglars broke into the Walnut Creek, California, offices of Colt Express Outsourcing Services, stealing equipment "which contains the human resources data of several of their clients including CNET networks," CNET Senior Vice President of Human Resources Jose Martin said in a June letter notifying employees of the incident.

The computers contained names, birth dates, Social Security numbers and employment information of the beneficiaries of CNET's health insurance plans.

It was unclear which other Colt Express clients were affected by the breach. Its other customers have included BroadVision, JDS Uniphase and 24 Hour Fitness.

The company's CEO, Samuel Colt III, did not return a call seeking comment Monday, but in a letter to CNET, published on the Web site of the attorney general for the state of Maryland, he said that local police were investigating the matter.

Data breaches such as Colt's must be reported to the Maryland attorney general when they affect state residents. State laws typically require such notification when an unencrypted computer is lost or stolen. According to Privacy Rights Clearinghouse, more than 230 million records have been exposed in this fashion in the U.S. over the past three-and-a-half years.

Four days after the break-in, Colt Express installed an alarm system, and the company is "looking into what additional steps may be taken to provide enhanced security," Colt wrote in his letter.

Customers looking for free credit-monitoring services from Colt Express should not get their hopes up, however.

Colt's letter included some marketing materials for Kroll, a company that helps companies respond to data breaches, but the information was provided "only out of courtesy and to give you an idea of the types of services available," Colt said.

"By this letter and enclosures we are providing you with all the information we believe you need and that we are able to give you," Colt added. "We do not have the resources financial and otherwise to assist you further."

Hurt by a downturn in business late last year, Colt is now in the process of going out of business, he said.

Affected CNET employees can sign up for one year of free credit-monitoring from Equifax, Martin said.