At around 9:50PM EST, CloudFlare (our CDN provider) started serving minified content from another website (not ours).
Access to BetterTTV is now restored, but if you still are having issues you will need to clear your browser’s cache and refresh any open Twitch pages.
A ticket is in witch CloudFlare to hopefully help them prevent this from happening again (or to anyone else).
edit: CloudFlare confirmed that the issue has been fixed on their end.