A common way to notice things like this is to subscribe to a service like Renesys or Cyclops (http://cyclops.cs.ucla.edu/ http://cyclops.cs.ucla.edu/) that will

A common way to notice things like this is to subscribe to a service like Renesys or Cyclops (http://cyclops.cs.ucla.edu/ http://cyclops.cs.ucla.edu/) that will alert you if it sees your subnets being announced by a different AS.