In an interesting discussion over at NamePros, the owner of the domain name Poets.net describes how her domain – registered at Register.com – appeared to forward random subdomains to parked pages controlled by the registrar.
We don’t own any domains at Register.com to verify this odd behavior.
This practice is called “wild-carding“; the capturing of any third-level domain traffic and its subsequent forwarding.
Read more at the NamePros thread.