US first lady Michelle Obama and vice president Joe Biden are among the latest public figures to have their private information posted on a mysterious website.
The Secret Service has joined the investigation into the postings that include documents from people ranging from rapper Jay-Z to the head of the FBI.
The site includes identification numbers, credit reports, addresses and phone numbers.
It bears an internet suffix originally assigned to the Soviet Union and many of the pages feature unflattering pictures or taunting messages of the person featured.
Others whose information is posted include pop star Britney Spears, US attorney general Eric Holder, former Republican candidate for vice president Sarah Palin and Terminator star Arnold Schwarzenegger.
Both the FBI and the Secret Service said they were investigating the site.
White House press secretary Jay Carney said he had "no assessments to offer" on the situation and referred questions to the Secret Service, which would not provide further details.
The site grew from 11 names to 18 in the first 24 hours since it became public, with its operator adding additional features to count the number of visitors and a link to a Twitter account. It offers no explanation about why the targets were selected or how the information was obtained. The Twitter account includes an anti-police message in Russian.
President Barack Obama told ABC News that he was aware of the investigation.
"We should not be surprised that if we've got hackers that want to dig in and have a lot of resources, that they can access this information," he said. "Again, not sure how accurate but ... you've got websites out there that tell people's credit card info. That's how sophisticated they are."