https://arstechnica.com/tech-policy/2019/12/us-ethereum-developer-arrested-for-violating-north-korea-sanctions/

The prominent hacker and Ethereum developer Virgil Griffith was arrested by the US government Friday after he spoke at an April conference on blockchain technologies in North Korea. The US government considers his presentation to be a transfer of technology—and therefore a violation of US sanctions.

But Griffith's defenders, including Ethereum founder Vitalik Buterin, describe the arrest as a massive over-reaction. Griffith worked for the Ethereum Foundation, and Buterin called him a friend.