Good point.  Depending on the strength of the cryptographic attack, let's supposed 100 blocks where solved in an hour.  It would raise a lot of suspicion since 100 is a lot.  The bitcoin client would then readjust the difficulty level and all other miners would not solve very many blocks.  Miners would complain and most likey the bitcoin dev team would change the algorithm.

But, if 10 blocks were solved in an hour and then the difficulty adjusted it could have been pure luck and there would be no sure fire way to prove it without mathematical proof.

I don't think breaking sha256 is "hacking".  It's like a gold miner finding the motherload.  However, I think breaking EC would be hacking.