FBI agents have searched the property of at least 10 people suspected of involvement in electronic break-ins at the US data broker LexisNexis.
Agents removed computer equipment from buildings in California, Minnesota and North Carolina, the FBI said.
No arrests have been made, but it is feared that the stolen data could be used by criminals for identity fraud.
LexisNexis said in April that hackers may have gained access to personal details for many thousands of people.
It announced that a series of incidents over the past two years had exposed information on 310,000 US citizens.
One of those whose properties were searched told the Washington Post: "They came looking for anything connected with LexisNexis."
Zach Mann, 18, of Maple Grove, Minnesota, said FBI and Secret Service personnel removed personal computers and dozens of computer disks from his home on Monday.
Jason Hawks, 23, of Winston-Salem, North Carolina, told the newspaper: "They busted down the door and ran at me with guns pointed in my face."
Paul Bresson, an FBI spokesman in Washington, said the bureau was investigating whether the breach was related to the theft of data from a mobile phone owned by celebrity heiress Paris Hilton.
Recently notes and celebrity contact details, apparently from Ms Hilton's phone, were published on websites, as well as topless photos of her.
The Washington Post said a third person raided by the FBI - who cannot be named because he is under 18 - had told the newspaper he was involved in both the Paris Hilton and LexisNexis break-ins.
Concerns about electronic security have prompted the US Congress to consider greater regulations for the industry.
In February, it was revealed that hackers had been able to access the vast database held by a LexisNexis rival, the ChoicePoint credit reference agency. SOURCE