More than three million WordPress sites which are currently running that “All In One SEO” plugin will need to be updated to resolve a set of vulnerabilities that could be used to hijack sites. As is often the case, the troubles were found and reported by the researchers at WordFence. And as I've also noted before when we were talking about the inherent danger of 3rd-party developed WordPress add-ins which appear to be having constant security problems, adding protection from WordFence, if it fits your budget, would seem like a large and worthwhile ounce of prevention