Poor Bing. Microsoft's search engine has been having quite the challenge in trying to inch closer to Google's marketshare, and incidents like this ongoing one do little to help. If you try to visit the secure version of Bing (using https:// instead of http://) right now, you'll be greeted to an error instead of the website. You can see an example of the error in the image below, which was captured with Google's Chrome. Any Web browser will issue a similar warning.
It'd be easy to jump on the "Microsoft is too inept to handle SSL certs!" bandwagon, but this issue actually has nothing to do with the Redmond company. Instead, the blame falls (likely) entirely on its content delivery system, operated by Akamai, as the error above again states. It's not only Bing that's having issues, either; NBA's official site is experiencing the same issues (as of the time of writing, it's not even issuing an error, so it seems SSL has simply been disabled.
If there's a lesson to learn here, it's that third-parties can mess-up and cause your business to halt - but that's hardly been an unknown. What is a bit surprising here is that the issue hasn't been fixed already - it's been ongoing for at least two days.