It actually was not the OS that was hacked. Both target MacBook Pros fended off the hackers until the rules were relaxed and the USERS of those computers were required to navigate to a hacker setup malicious webpage... and a newly discovered security vulnerability in the browser application was exploited.
This is being reported to Apple and the application will be patched.
And your saying that the MAC OS is not hackable? It is totally immune to hacking?