China’s Great Firewall, used by the government to regulate access to foreign internet sites, has blocked one of the most popular sources of ethereum blockchain data.

As of Tuesday, etherscan.io, one of the longest-running and most widely used ethereum block explorers, was inaccessible from IP addresses inside mainland China, based on tests performed locally.

The change appears to be recent. According to Greatfire.org, which compiles and monitors a database of sites that are blocked inside China, etherscan.io was still accessible with “no censorship detected” as of Aug. 18, 2019.

But Greatfire.org’s scanning record shows etherscan.io has become 100 percent blocked since at least Oct. 30, rendering it inaccessible from inside China unless via a virtual private network (VPN).

This is likely the first known case of a blockchain explorer becoming an internet firewall target and puts etherscan.io in the company of such blocked information and social media sites as Google, Facebook, Twitter, and Reddit.

“This is another instance of friction between the decentralized and immutable technology of blockchain and the tightly controlled, centralized government of China,” said Matthew Graham, CEO of blockchain investment firm Sino Global Capital. “We should expect additional problems like these in the future as blockchain is integrated further into the Chinese economy and daily life.”

Reasons unclear

It’s not immediately clear what exactly led to the blocking of a blockchain explorer in China. But last year, there were reports that cryptocurrency users encoded censored articles regarding the #Metoo movement and a pharmaceutical scandal in China onto ethereum transactions in a bid to bypass internet censorship.

Internet users had been sharing on WeChat the hash of those transactions using etherscan.io, which even prompted WeChat to later block users from viewing the exact etherscan.io URLs from inside the messaging app. Etherscan.io’s site itself remained intact at the time.

“Some have used this feature to post sensitive messages without the need to worry about the message being blocked or removed, or their identity being exposed,” said Graham. “Anyone with a blockchain explorer like Etherscan can view these messages, so it is not surprising that this website has come in the crosshairs of internet censors.”

Matthew Tan, founder and CEO of etherscan, said his firm noticed the block ”within the last 3 months” but was unsure of the exact date. He said he doesn’t know why this occurred and thus “can not speculate on what the reasons might be.”

Greatfire's test of etherscan.io Source: Greatfire.org

Substitute site

There is evidence that the blockage may have happened sometime in September and went largely unnoticed.

For instance, MakerDAO, the decentralized finance project, switched from using etherscan.io in a WeChat post in Chinese on Sept. 16 to using a new etherscan site – cn.etherscan.com – in another post on Sept. 30. The new site, which appears identical to etherscan.io, is currently accessible from inside China.

To be clear, a blockchain explorer is merely an online portal that makes it easier for end-users to browse transaction information of a decentralized network. The actual blockchain transactions are not stored in any centralized database and thus can’t be taken down by a single entity regardless of geographic locations.