Chinese police have arrested roughly 15,000 people for crimes they claim “jeopardized Internet security,” Reuters reports.

The roundup is part of the government’s ongoing efforts to tighten Internet control, which includes a recent national security law that gave officials vague authority to secure and control the country’s computer systems.

{mosads}According to China’s Ministry of Public Security, police investigated 7,400 instances of cyber crime over an indefinite period that led to the arrests.

Officials said they looked into more than 66,000 websites offering “illegal and harmful information,” in addition to those with advertisements for pornography, explosives and firearms, and gambling.

Since taking office in late 2012, Chinese President Xi Jinping has spearheaded an unprecedented crackdown on the flow of digital information into and within China.  

Beijing officials operate a massive censorship operation, known as the Great Firewall, which blocks websites and digital services that disseminate information critical of the Communist Party.

Officials have also reportedly used the mechanism to snoop on dissidents and foreigners.

The ongoing campaign has irked the U.S., which is expected to press Xi on his digital controls during the leader’s upcoming Washington visit.