Federal regulators are investigating whether telephone companies are doing enough to keep customers' records from falling into the hands of unscrupulous online data brokers.

"These records can include some of the most private personal information about an individual," Jonathan Adelstein, a commissioner at the Federal Communications Commission, said Tuesday. "Finding out who people are calling and for how long can be like picking someone's brain about their friends, plans or business dealings."

Fellow Democratic Commissioner Michael Copps also praised the FCC's inquiry. "This must be a priority because every day such a problem exists puts American citizens needlessly at risk," he said.

The head of the commission, Kevin Martin, revealed the investigation in a letter last week to Rep. Ed Markey, D-Mass., who has complained about the practice.

Martin said the agency was looking into how the online companies are getting the private records. The agency is coordinating its efforts with the Federal Trade Commission, he said.

In a letter to the FCC and the FTC last November, Markey said the disclosure of phone records without a customer's consent is illegal, and he asked the agencies what they are doing to shut down these operations.

Markey cited concerns about the sale on several Internet sites of customers' wireless and landline phone records, including the date, time and length of calls placed by consumers.