An anonymous reader writes with this excerpt from Help-Net Security (based on the linked Trend Micro report): "Every country's cybercriminal underground market has distinct characteristics, and with 500 million national mobile Internet users and the number continuously rising, the Chinese underground market is awash with cyber crooks buying and selling services and devices aimed at taking advantage of them. Trend Micro's senior threat researchers Lion Gu has been scouring forums, online shops and QQ chats to give us a sense of what is actually going on on this burgeoning mobile underground. Mobile apps that stealthily subscribe users to premium services are, naturally, very popular with cyber crooks in China as in the rest of the world. Premium service numbers can also be bought on underground markets. Network carriers usually assign premium service numbers to qualified service providers, but obviously some of them are not [averse to] selling them on to criminals."