Twitter permanently bans former KKK leader David Duke

• It's not immediately clear which tweets triggered Duke's account to be banned. He was banned from YouTube in June.
• Twitter revised its code of conduct in March, prohibiting posts that promote violence or threats of violence against people based on their religion, race or ethnic origin.

The big picture: Social media companies have been under fire from big-name advertisers for not doing even to combat hate speech and misinformation on their platforms.