A few weeks ago we rolled out Content Security Policy on CodePen. You can read more about CSP here. It's technology in modern web browsers that helps increase security.
<script>alert(document.cookie);</script>). We do everything we can to prevent scripts from being injected anywhere on CodePen, and will continue to, but if something slips through, it can't execute anyway in browsers that support CSP. That's a pretty nice security upgrade!
If you happen to notice anything behaving funky after this change, definitely let us know. There were some warts right after it went out and there might still be a few. For instance, we just fixed on where Instapaper wouldn't work on blog posts, because CSP was stopping the script (fixed now).