Just a warning to people that have attempted to update OS X apps today. Apple's SSL certificate for swscan.apple.com expired last night at midnight, and it seems they neglected to renew it. Thus, many users are experiencing errors when downloading appps. Clicking ok on the dialogue will allow you to download non-Apple app updates, but not system updates or apps created by Apple, at least temporarily.
For more information, se this 9to5 Mac Article