Police in east China have announced their arrest of 20 members of a gang they say traded in 700 million pieces of personal information stolen from two government databases.

Getting to the bottom of this massive personal data leak from a medical service information system and a provincial poverty alleviation website took the police in Lishui, Zhejiang Province 13 months, they told CCTV. In an investigation spanning multiple provinces, they identified two hackers behind the breaches.

Illegally-sourced information like this is often used to commit crimes like telecom fraud and extortion.

Chinese authorities have been working to make personal data more secure and to catch and punish hackers. According to the Ministry of Public Security, 2016 saw police investigate 1,800 data-leak cases and arrest 4,200 suspects. Those detained included 390 internal staff of companies and entities holding the information, and nearly 100 hackers.

Apart from cyber-attacks, the ministry also warned that data leaks commonly occur when people give out their information voluntarily while job hunting, to dating agencies, or during membership sign-ups. 

Fraud groups also trap personal information through fake website links.

The ministry urged administrative bodies, organizations or companies that hold large amounts of public data to strengthen measures ensuring its security. The public should also be alert when sending requests to unknown servers, and be more wary about giving out information like their names, birth dates, phone numbers and locations.

China amended the law last year so that people selling or illegally providing personal information face between three and seven years in prison and a fine.