Twitter permanently bans former KKK leader David Duke

Twitter on Friday permanently banned former Ku Klux Klan leader David Duke for violating the platform's rules on hate speech, AP reports.

Why it matters: The Anti-Defamation League describes Duke as "perhaps America's most well-known racist and anti-Semite."

• 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.