Residents in China have found logging into their Facebook and Twitter accounts increasingly difficult in recent days, after several popular VPN (virtual private network) companies have alleged that China's Great Firewall (GFW) has been upgraded. However, officials and experts in China's Internet industry have said that it is illegal for foreign companies to operate a VPN business in China.

Three overseas VPN service providers, Astrill, Witopia and StrongVPN apologized Thursday that their service to residents in the Chinese mainland has been blocked due to a recent upgrade of the GFW. Astrill claimed that most VPN protocols have been blocked,  and that many foreign companies have been influenced.

Fang Binxing, designer of the GFW, told the Global Times Thursday he did not know of any upgrade to the firewall. 

"As far as I know, companies running a VPN business in China must register with the Ministry of Industry and Information Technology. I haven't heard that any foreign companies have registered," Fang said.

Unregistered VPN service providers are not protected by Chinese laws, and any company running a VPN business should realize they have a responsibility to register, he said.

An employee from the Ministry of Industry and Information Technology, surnamed Li, also confirmed that only Chinese companies and Sino-foreign joint ventures can apply to establish a VPN business.

While most VPN users in China only use a VPN to access certain websites, some multinational companies also use it to conduct business operations.

An executive at a large foreign technology multinational corporation in China, who is also a VPN user, told the Global Times most people can survive without Facebook, but lacking a VPN could seriously influence business operations.

"You can't block all VPNs without blocking businesses, including Chinese businesses. China wants businesses to put regional headquarters in China. It has these economic and business goals that are reliant on modern business infrastructure," said the executive.

Li suggested that multinational corporations should cooperate with local companies to build up their VPN networks to complete their own global communication networks.

"These companies should follow Chinese laws and find licensed local companies to establish their Chinese VPN networks," she said.

Martin Johnson, founder of GreatFire.org, a website which monitors the Internet in China, told the Global Times Thursday that  there are still ways for Web users to access their favorite websites.

"Even if VPNs are blocked, foreigners and Chinese citizens can still use a range of tools to get around this," he said.