A man who allegedly tried to sell the user data of 600,000 rail passengers for a mere $20 is under criminal detention, police said this week.

Police said the man had illegally purchased the data, and then attempted to sell the information online for $20.

The data up for sale included real names, ID numbers, phone numbers and email addresses of passengers, local media reported. 

Police also said the man used the data to find the contact information of an additional 4.1 million people who were connected to the original compromised accounts.

The leaked data originated from state-owned China Railway's ticketing platform 12306.cn. China Railway initially denied there had been a leak on its platform. The company has not commented since police announced the arrest.

Stolen info comes cheaply in China. The data of 5,000 online lending users were sold for $60 in December, local media reported.