triock: Yeah, it's a common problem for many Mac users.
Solution can be found in Support section, but in these case it's a little bit tricky as those games are no longer on GOG, so I choose another game. But don't worry, solution is the same for all games. ;)
http://www.gog.com/support/fahrenheit_indigo_prophecy/ibread_first_mac_os_xb_faq_and_solutions_for_known_issuesi Game "is damaged and can't be opened. You should move it to the Trash."
a) Redownload the game using the newest version of the GOG Downloader:
https://secure.gog.com/downloader To download, make sure the "GOG.com Downloader mode" is switched to ON before clicking the "Game installer" button. After the download is complete, reinstall the game.
b) Use this workaround if using the Download didn't help:
- Go to Applications -> Terminal
- Type in:
xattr -d com.apple.quarantine
but don't press Enter.
- Drag the application to the Terminal window, this should add the path.
- Press Enter.