It is a TCP server running on the Wii that listens on port 8080 and will run any binary that is sent to it after you confirmed the IP address with your GC controller. An additional warning is displayed when the connection comes from the internet (i.e. the first two octets of your Wii's ip does not match the first two octests of the connector's ip). Both DOL and ELF executables are supported.
You currently need libogc cvs to compile this yourself from the source code.
Download (linux binary and Wii server)
The client first sends the length of the file to load in big-endian int32 and then the data of the file. There is no traffic from the server.