Doyle Rice

USA TODAY

China recently hacked into U.S. weather and satellite systems, forcing cybersecurity teams to seal off vital data, officials said Wednesday.

The news comes two days after the U.S. Postal Service announced it had been hacked — also reportedly by the Chinese. Wednesday, President Obama and Chinese President Xi Jinping announced a climate change agreement in Beijing.

The National Oceanic and Atmospheric Administration (NOAA) confirmed the attack but did not indicate the source of the breach. However, the agency told Rep. Frank Wolf, R-Va., that China was to blame, Wolf's spokesman, Dan Scandling, said.

Wolf, who heads the U.S. House subcommittee that funds NOAA, also scolded the agency for not disclosing the breach to the public.

In recent weeks, four NOAA websites were compromised, spokesman Scott Smullen said. "NOAA staff detected the attacks, and incident response began immediately," he said.

The Washington Post, which first reported the attack, said the initial breach was in September, but government officials gave no indication of the problem until Oct. 20.

The Chinese may not have been trying to acquire specific data in either attack but could have been looking for a way into U.S. computer systems to see how unclassified portions of the U.S. government function, said Edward Ferrara, an analyst with technology research firm Forrester.

Even as Obama shook hands with China's president, an unspoken cyberwar continued to run between the two nations, Ferrara said.

"Functionally, we're in a spirit of détente with the Chinese. We're talking with them and trying to cut deals with them, but we're both hitting each other with two-by-fours in the background," he said, adding that the United States maintains the ability to penetrate China's system.

The weather satellite data include forecasts and warnings vital to Americans and the U.S. economy, University of Georgia meteorologist J. Marshall Shepherd said in an e-mail.

"The Chinese hacking of our weather system illustrates that they also understand the value of this data and information," he said. "Every corner of our lives depends on weather information."

NOAA said it performed unscheduled maintenance to mitigate the attacks, but all services have since been fully restored. The agency wouldn't provide details on what was attacked, whether anything was removed, whether malicious software was let loose in the system or how long the maintenance took after the attack.

"These effects did not prevent us from delivering forecasts to the public. The investigation is continuing with the appropriate authorities, and we cannot comment further," Smullen said.

The Chinese could have just been testing U.S. defenses. University of Washington meteorologist Cliff Mass said he's not sure what China would get by harming the U.S. weather network. Though the Chinese have weather satellites, they also use U.S. data in their forecasting, he said.

"The Chinese are as dependent on the weather satellite data as we are," he said. "They would undermine their own weather prediction if the satellite data was not available."

The weather satellite hack comes two days after The Washington Post reported China may have been involved in the Postal Service cyberattack, citing anonymous sources. USA TODAY was unable to confirm the report.

The perpetrators behind that breach penetrated the post office's employee database, compromising information about more than 800,000 workers, according to the Postal Service. They also got into the service's customer care call-in and e-mail service.

Contributing: Elizabeth Weise, USA TODAY, from San Francisco