After U.S. computer-security firm Mandiant Corp. accused China of stealing large swaths of data from U.S. companies, China flatly denied the accusation. In a 74-page report, the firm claims a group attached to China’s People’s Liberation Army stole data from 141 companies since 2006, 115 of which were in the U.S., spanning industries like information technology, telecommunications, aerospace and energy.

Chinese Foreign Ministry spokesman Hong Lei denied the accusations during a daily news briefing on Tuesday. “Cyberattacks are anonymous and transnational, and it is hard to trace the origin of attacks, so I don’t know how the findings of the report are credible,” he said.

“At the same time, Mr. Hong said China has been a frequent victim of cyberattacks, and he added that the U.S. has been the top source of such attacks,” reports the Wall Street Journal. “China has suffered virus attacks, and Chinese personal computers have come under control by foreign Internet addresses, he said.”

Asked if he believes that the U.S. government was behind such attacks, Hong said: “we can only say they originated in the U.S.” He added that this was “entirely different from media reports that the Chinese government or the Chinese military are responsible” for the attacks detailed in Mandiant’s report.

“The Chinese military has never supported any kinds of hacker activities, so saying that the Chinese military is involved in Internet attacks is neither professional nor consistent with the facts,” said China’s Ministry of National Defense.

But concerns are present in the U.S. as Defense Secretary Leon Panetta said China was “rapidly growing” its cyber capabilities. “In my visit to Beijing,” he explained, “I underscored the need to increase communication and transparency with each other so that we could avoid a misunderstanding or miscalculation in cyberspace.”

According to Mandiant, the group behind the hacking is called “Unit 61398, within a wing of the People’s Liberation Army. It said it has observed hacking attempts against nearly 150 victims over seven years. Hundreds of terabytes of data were involved, it said,” writes WSJ.