It looks like perhaps it was a myth.
According to root-servers.org:
There are multiple documented instances of middleboxes interfering with root server system traffic. However, we believe this is the first documented case where routes to root server prefixes were hijacked using BGP.
Bummer.
Edit: This article describes an attack this year. I was thinking of an older one.

There are two types of marshmallow roaster inside me...