Police in China say they have arrested about 15,000 people for crimes that “jeopardised internet security”, as the government moves to tighten controls on the internet.

Police have investigated 7,400 cases of cybercrime, the ministry of public security said. It did not make clear over what period the arrests were made, but referred to a case dating to last December.

Last month China launched a six-month programme codenamed “Cleaning the Internet”. “For the next step, the public security organs will continue to increase their investigation and crackdown on cybercrimes,” the ministry said.

The sweep targeted websites providing “illegal and harmful information”, or advertisements for pornography, explosives and firearms and gambling. In total, police investigated 66,000 websites.

China runs one of the world’s most sophisticated online censorship mechanisms, known as the Great Firewall. Censors keep a tight grip on what can be published, particularly material that could potentially undermine the ruling Communist party.

In February China’s internet watchdog said that from 1 March it would ban internet accounts that impersonate people or organisations, and enforce a requirement for people to use their real names when registering online accounts.