Hacking attacks on Chinese computers in 2013 rose by more than half compared with the previous year, with attacks coming from the United States making up a significant proportion, China’s top Internet security agency said on Friday. Beijing and Washington have been squaring off for months over the issue of cyber attacks, each accusing the other of hacking into sensitive government websites. China has long singled out the United States as the top source of intrusion on its computers. China’s National Computer Network Emergency Response Coordination Centre, said the country’s Internet faced “many security threats”, creating a “challenge” for China’s overall security.