In the last 10 days, China has been tightening its grip on the Internet, blocking several tools that allow users inside the country to escape and circumvent what's popularly known as the "Great Firewall of China."

Some popular Virtual Private Networks, or VPNs, were the latest victims of the sophisticated Chinese Internet censorship system, with several individuals and small businesses reportedly unable to use them in the last few days to connect to censored websites, or to use other blocked services like Gmail, Flickr or Twitter.

But not all hope is lost for Chinese users trying to get around the Great Firewall.

"It's wrong to report that all the VPNs have been shut down, and that all the circumvention tools have been shut down," Charlie Smith, one of the founders of the Internet censorship watchdog GreatFire, told Mashable.

In fact, the block has affected only popular, commercial VPNs such as Astrill, StrongVPN and Golden Frog.

Just got this note from Astrill (VPN service) pic.twitter.com/OPH5WACUle — Megha Rajagopalan (@meghara) January 24, 2015

Other alternative, less widespread tools, such as Psiphon, Lantern, Tor, and other VPN services, in fact, remain active.

Moreover, on Friday, two of the affected VPNs announced that they were able to fight back and restore their services, at least partially.

Golden Frog announced it in a blog post, while StrongVPN confirmed it to Mashable via email.

Yet, China's new crackdown on circumvention tools is almost unprecedented, or at least the worst since 2012, according to Bill Bishop, an American who lives in Beijing and is the editor of the influential Sinocism newsletter.

"Their vision is to create effectively one world, two Internets", Bishop told Mashable, referring to the Chinese government, "where they have the Chinese Internet and they have the rest of the world. There are still links but they seem to be squeezing them tighter and tighter."

China seemed to confirm the crackdown on Tuesday, when Wen Ku, an official at the Ministry of Industry and Information Technology said that China "needs new methods to tackle new problems,” and that the "development of the Internet has to be in accordance with Chinese laws," according to the government's People's Daily.

China has always been very aggressive in trying to control the Internet (sites like YouTube, Facebook and Twitter have long been unavailable), but this crackdown on VPNs is the latest episode in a recent spike in online censorship and surveillance.

In the last few months, China has implemented several measures to block Google services.

Activists and cybersecurity experts have accused the government of being behind intrusive cyberattacks designed to surveil citizens using Yahoo, Microsoft, and Apple services. The government has always denied all accusations.

Yet, the biggest question after China's block on VPNs is: why now?

China has always had the ability to block at least some VPN traffic, according to experts consulted by Mashable, so the reasons behind this latest crackdown might be political. In fact, ever since Lu Wei, China's Internet czar, rose to power, the country has ramped up its censorship capabilities.

President "Xi Jinping says 'we have to take measures to control the Internet,' and this guy is taking those measures," Smith said. "This guy has really got the power, and is moving forward to take control of everything about China's Internet."

The Chinese embassy in Washington D.C. did not respond to Mashable's request for comment.

For Bishop, the VPNs that got blocked perhaps became too popular among Chinese users, and the government might have felt it had to step in.

After suffering disruptions, Astrill mocked China's censorship system last week in a series of tweets.

After #Astrill VPN service shut down in China, here is what intents to do - essays sent to censors ministry pic.twitter.com/pVSkufyW2M — Jennifer Zhu Scott (@jenzhuscott) January 23, 2015

The tweets have since been removed, and Astrill did not respond to a request for comment.

Perhaps, this was all just a warning to VPNs operating in China, just a way for the Chinese government to assert its power and show that, if they want, they can block some of these services. Tools like Psiphon and Lantern were perhaps spared by obfuscation techniques, which makes it harder for censors to detect the use of these tools.

Other VPNs, if they haven't already, will have to follow suit in a seemingly never-ending cat and mouse game.

This story has been corrected. A previous version mistakenly said that Astrill sent the mocking tweets before getting shut down. The tweets, in fact, were sent afterwards