A microblog service launched Tuesday by the Web site of the People's Daily, the mouthpiece of China's ruling Communist Party, added to the growing number of Twitter-style services offered in China but became inaccessible by Wednesday. Screenshots posted in Chinese online forums showed the service before it went offline bombarding visitors with a set of pop-up messages apparently added by a hacker.

Some were satirical notes about the state-run newspaper or the "Great Firewall of China," an informal name for the set of Internet controls China uses to block Web sites like Twitter, Facebook and YouTube.

"The People's Daily Online has been conquered by the people," one of the messages said. "If you see this message it means you you may be victim of the [Great Firewall], please quickly immigrate or topple it," said another.