The secret message was included in the last block before the halving, by F2Pool, a major mining pool that specializes in Bitcoin, Ethereum, and Litecoin. F2Pool mined block 629999 on May 11 at exactly 19:23. It was the last block to carry a 12.5 BTC reward.
The message is a reference to an article posted by the New York Times on April 9. According to the article, the Federal Reserve pumped up to $2.3 trillion into the economy in response to the Covid-19 crisis.
The halving happens once in four years and sees Bitcoin’s block rewards cut by 50%. The event is bitcoin’s unique way of controlling inflation. Although this is bitcoin’s third halving, it is the first time a secret message was embedded at a halving.