4 Must HTTP Security headers

1. Content Security Policy
   For restrict the origin
2. X-Frame-option
   Stop Clickjacking
3. X-Content-Type-Options
   Control file uploads
4. Strict-Transport-Security
   Never jump to http

Source: http://www.ibuildings.com/blog/2013/03/4-http-security-headers-you-should-always-be-using