The Ministry of State Security said a Taiwan military-backed hacking group has been carrying out cyberattacks against targets in China, urging people to report "anti-propaganda sabotage".

The ministry said since the beginning of this year, Anonymous 64 had sought to upload and broadcast "content that denigrates the mainland's political system and major policies" on websites, outdoor screens and network TV stations.

In a blog post published on its official WeChat account, the ministry said its investigation into the group had found many of the websites Anonymous 64 claimed to have accessed were fake or had little to no traffic.

Posts showing it having infiltrated numerous university and media websites had been photoshopped, the ministry added.

Officials also said they had opened a case against three members of Taiwan's cyber warfare wing.

"We advocate that netizens should not believe in or spread rumours and should promptly report cyberattacks or cases of anti-propaganda activity to the national security authorities," the blog post said.

Taiwan authorities have denied the hacking allegations. (Reuters)