note joels careful use of 'injected'. imiho, 'hijacked' is perjorative implying evil intent. i very much doubt that is the case here. it looks much more like an accident. could we try to be less accusatory with our language. 'injected', 'mis-originated', ... would seem to descrive the situation.
and, btw, how many of those whose prefixes were mis-originated had registered those prefixes in the rpki? randy