Researchers at one of China's top universities collaborated with a Chinese army unit accused of carrying out hacking attacks on the United States, academic papers published online show.The elite Shanghai Jiaotong University conducted network security research with People's Liberation Army (PLA) Unit 61398, the co-authored papers, accessed by AFP, reveal. A US security company said last month that the army unit, also based in China's commercial hub Shanghai, was behind serial hacking attacks on US firms, sparking a war of words between the two powers. Last week US President Barack Obama raised cybersecurity with China's new President Xi Jinping. China has denied that it engages in hacking and claims its military is a victim of cyberattacks mostly originating in the US. Several researchers at Shanghai Jiaotong's School of Information Security Engineering (SISE) published research with members of Unit 61938, with projects dating back to 2007, the papers easily accessed online show. Subjects of the joint research include the design of an "intrusion monitoring system" for computer networks and ways to evaluate "attack graphs," which show how an adversary can break into a computer system. None of the papers described plans to carry out cyberattacks on foreign targets. The university was not immediately available for comment on Sunday. Xue Zhi, a co-author of one of the papers and SISE's vice-president, is the developer of China's leading "cyber-penetration attack platform," according to the university's website. Shanghai Jiaotong University is one of China's flagship educational institutions, and has attracted members of China's business and political elite, with former President Jiang Zemin amongst its alumni. The US Department of Defence has approved a fivefold expansion of its cybersecurity force to include 4,900 troops and civilians over the coming years in response to growing online threats, The Washington Post reported in January.