WifiMe uses the Wireless MultiBoot protocol to send an RSA signed game to the DS.
Two copies of the header are sent in the protocol.
One copy of the header is used to display a list of available games to download.
The other copy is used when the DS checks that the signature is correct.
When the DS decides which start addresses to use it uses the first header.
WifiMe makes the same header modifications as PassMe1, redirecting the ARM7 to the GBA slot and putting the ARM9 in an infinite loop.
How Nintendo Stopped WifiMe From Working
Nintendo modified the firmware in the DS so that it uses the start addresses in the signed header.
The signed header cannot be modified without knowing Nintendo's private key, so WifiMe is not possible unless you have an old DS.