The Premium SEO WordPress plugin is malicious: it ships an unauthenticated backdoor that creates a hidden administrator account and, in some builds, also enables remote code execution, server-side request forgery and arbitrary front-end script/content injection, giving an unauthenticated attacker full control of the affected site.
https://wpscan.com/vulnerability/0115a640-7139-4ef9-81be-6ee5c755a601/