A Microsoft cloud computing platform recently released an urgent notice requiring its customers to shut down their virtual private network (VPN) services in China. Microsoft Azure, an open and flexible cloud computing platform, said on its official website that according to the telecom regulations and requirements of China's Ministry of Industry and Information Technology (MIIT) and Internet supervision agency, no company or individual can provide hosting service for illegal "over the wall" proxy sites or illegally mount any VPN service abroad.

"Recently, the regulators have found that several Windows Azure customers violated the related regulations and demanded the immediate shutdown of service deployment. We will continuously receive notification from the regulators to close such sites or shut down service deployment," read the notice.

"China has tightened its supervision of the sales of VPN services, and several VPN providers told me that their websites have been shut down," William Long, a Chinese tech blogger, told the Global Times on Thursday.

According to Chinese law, providing VPNs for individual users for the purpose of accessing banned websites is illegal on the Chinese mainland, while offering VPNs for corporate use is legal.

A cyber security analyst noted that companies running VPN businesses in China must register with the MIIT, adding that unregistered VPN service providers are not protected by Chinese laws.

China's Internet authorities said in January 2015 that "improper information" online will be regulated according to Chinese law amid worries about the unavailability of overseas VPN services.

Wen Ku, director of the communication development department at the MIIT, told a news conference that "Internet development in China should be in line with the law, and some improper information should be regulated."