This is becoming so frustrating. Software Update fails, all Apple DMGs fail to mount (with various errors) and I cannot download anything from iTunes. I've followed forum after forum, trying various work arounds but still I'm having no success. I've restored my computer to factory settings twice, tried manual download of Software Updates but cannot mount as the file is corrupt, accessed private/etc/hosts and adding 18.104.22.168 swcdn.apple.com. I've read somewhere that the problem could be with a new router - as this was replaced at the same time, but I can't install old router and we got rid :S I'm at the end of my tether... can someone help at all? I really don't know what to do.