could the OBDII response, be faked?

Could the obdii response, when challenged by the
computer at the emmissions place, be replaced with
a general purpose computer, given the istructions
to repond with... everything is OK.
.
How much security went into making the thing hack resistant?
Does the emmissions testing place call up GM,
and get some type of secret hash function?

if you could responde with the correct information, there would be noway for them to know....i guess you would just have to find out what exactly they checck for at emmisions testing? DTC codes? and find out what the response is from your PCM if there are no DTC codes and duplicate that response, but it also has to "connect" to your PCM and you would have to fake all of those connection responses

I know in AZ, they check that the MIL light is working and responds to an error, then they read the pcm, waiting for a response....so hmm