They haven't made it hard; the phone-home is unauthenticated, so you could just spoof someone's DNS for instance. But even if a third-party exploit were imposs

They haven't made it hard; the phone-home is unauthenticated, so you could just spoof someone's DNS for instance. But even if a third-party exploit were impossible, it's a real problem if one company actually has a kill switch for 70% of Bitcoin's hashing power.