A look at some of American hacking accusations against China

Beijing: Accusations of hacking by China and Beijing's counterclaims of such activity by the US government have strained US-Chinese relations.

China has consistently denied cyberspying activities and says it too has been victimised by cyberattacks.

A look at some of the American accusations against China-based hackers:

Info on 4 million US Federal workers

American officials said Thursday that China-based hackers are suspected of breaking into the computer networks of the US government personnel office and stealing identifying information of at least 4 million federal workers.

A spokesman for the Chinese Embassy in Washington called such accusations "not responsible and counterproductive."

"Cyberattacks conducted across countries are hard to track and therefore the source of attacks is difficult to identify," said Zhu Haiquan.

The Office of Personnel Management was also targeted a year ago in a cyber-attack that was suspected of originating in China. In that case, authorities reported no personal information was stolen.

Pentagon cyberattacks

September 2014 - Senate investigators said that China's military had hacked into computer networks of civilian transportation companies hired by the Pentagon at least nine times, breaking into computers aboard a commercial ship, targeting logistics companies and uploading malicious software onto an airline's computers.

The report by the Senate Armed Services Committee blamed China's government for all the most sophisticated intrusions, although it did not provide any detailed evidence. It said China's military was able to steal emails, documents, user accounts and computer codes, compromise systems aboard a commercial ship and hack into an airline the US military used.

Military officers charged

May 2014 - US prosecutors accused China of vast business spying and charged five Chinese military officials with hacking into American companies' computers to steal trade secrets. The companies were big-name American makers of nuclear and solar technology. China objected strongly to the charges and called for a halt against what it called unscrupulous US cyber-spying, saying its own investigations "confirmed the existence of snooping activities directed against China."

Mandiant traces hacking to PLA

February 2013 - An American private security company claimed to have traced a massive hacking campaign against U.S. businesses to the Chinese military. After analysing breaches that compromised more than 140 companies, Mandiant concluded they could be linked to a drab, white 12-story building outside Shanghai run by the People's Liberation Army's Unit 61398, a secret Chinese military organization. China's defence minister called the Mandiant report deeply flawed.

Google closes China search engine

2009 - Google closed its mainland China search engine in 2009, saying it no longer wanted to cooperate with censorship after hacking attacks aimed at stealing the company's operating code and breaking into email accounts were traced to China.