So, how does one counterfeit a bitcoin?
Counterfeiting a bitcoin is essentially impossible, as far as anyone can tell. Bitcoin has been alive since 2010 and no hacker has ever been able to double spend (same as counterfeit) a bitcoin, despite numerous tries. Hacking the bitcoin protocol would be quite a feather in the cap of the hacker, allowing him to achieve worldwide notoriety, but it hasn't been done.
So, how does one counterfeit a bitcoin?
https://www.quora.com/Wont-it-be-easy-for-hackers-to-create-counterfeit-Bitcoins