I've had two people now tell me some problems, as well as a bunch getting it through well. I'm downloading myself now to check. As well as what Bob asked: Do you have the Mac version of civ? What error came up? How far did the install proceed? Anything else noteworthy about the progress? If the error is something about smartscreen or blocking then click proceed anyway (on Win 8.1 you need to go more info for that). It isn't malicious, they just base that around number of downloads/trusted source. Try checking the location it'll install to, and if it looks wrong then fix it.