You can think of them as the Bitcoin Santas. Every so often, they appear out of nowhere and bestow gifts on people across the globe, a bit like Santa Claus on Christmas Eve. The difference is that they always give bitcoins, the world’s most popular digital currency.

Late last year, they came to Yifu Guo. Guo runs Avalon, a company that builds and sells “Bitcoin miners,” specialized computers that help run the global open source software system that drives the digital currency.

They didn’t tell Guo who they were or where they were from. They merely said they were with an organization called Bitcoin Grant, and they asked him what his plans were for Avalon.