Mac App Store slips a receipt each time it is downloaded into the bundle. The receipt contains information about the computer used (the so called GUID) and the user logged into the App Store.
See here how you should validate the receipt: https://developer.apple.com/library/mac/releasenotes/General/ValidateAppStoreReceipt/Introduction.html#//apple_ref/doc/uid/TP40010573
If you implement the GUID validation as described in the document, the app will not run on any other computer.
Also check the signature of your code to make sure it has not been tampered: Verifying app's signature by code