Background:

• OSX (From Apple, or Hackintosh)
• The App was purchased from the App Store with the current iCloud ID

The problem:

• Unable to open a previously purchased App

The error:

“Magnet” is damaged and can’t be opened. Delete “Magnet” and download it again from the App Store.

It could be any paid app, in my case, ‘Magnet’.

There exist a similar but common error caused by unsigned/modified third party apps (blocked by Gatekeeper)

App Is Damaged and Can’t Be Opened. You Should Move It To The Trash

This is NOT what my guide is talking about.

The Cause

The error basically means Apple is unable to verify the App purchased on this machine.

The MAC address of your en0 is part of the verification. Because all Macs come with a built-in Wifi/Ethernet Adapter.

Run this in your terminal to list all network interfaces.

networksetup -listallhardwareports

What exactly happened to my is, my hackintosh motherboard comes with two built-in Ethernet adapters. I disabled one (en0) from the BIOS few days after the OSX is installed.

How to fix

If you encountered the same error message, try the following:

(Software issue, basically sync your current en0 MAC address with iCloud)

• Follow this guide from 1Password (also work for other apps from the App Store)
• If that doesn’t help, move on:

(Hardware issue. in most cases, en0 not found)

• list all network interfaces, find en0
• If en0 is not found, enable it from BIOS (if you disabled it before)
• If you didn’t remove/disable any network hardware, rename your primary interface to en0, here are some useful resources
  • Youtube Video
  • Guide from tonymacx86
• After that, follow the guide from 1Password again when necessary (when it’s still not working)

If none of those work:

Go to network settings > tiny gear icon > Set service order
Open a terminal and run:

cd /Library/Preferences/SystemConfiguration/
sudo rm NetworkInterfaces.plist
sudo rm preferences.plist
Restart machine

Credit for this: Jeremy Wininger