Web sites operated by the departments of Labor and Health and Human Services were working properly Sunday after being vandalized one day before by hackers who federal officials believe are from China.

A picture of Wang Wei, the Chinese pilot who was killed in a collision with a U.S. Navy spy plane April 1, was posted Saturday on Labor's Web site. Agency spokesman Stuart Roy compared the vandalism to graffiti: "You can lock up a store so the merchandise is safe," he said, "but you can't stop somebody running by with a can of spray paint."

Technicians had the site fixed within a couple of hours, Roy said, but on Sunday they were "still checking all the systems to make sure they weren't further penetrated."

Roy said the hackers were believed to be Chinese because of the content, including Chinese characters, they posted on the site.

HHS spokesman Bill Hall said a picture of Wang was placed Saturday on that agency's site. The surgeon general's site was disabled entirely.

HHS technicians added extra protections to the site's Web pages before putting them back online a few hours later, he said. "Our sites are as protected as we can make them," Hall said, "but you can never guarantee anything."

The FBI and the Federal Computer Incident Response Center are investigating Saturday's attacks, Roy said.

American hackers have vandalized scores of Chinese Web sites since the spy plane collision. Last week, the computer security firms Vigilinx and Symantec warned clients of possible retaliatory attacks by hackers from China around May 1, International Workers Day.