If you use the popular “All in One SEO Pack” WordPress plugin, you should update immediately. Two vulnerabilities and one cross-site scripting (XSS) flaw have been discovered.

Sucuri, a web monitoring and malware cleanup service was the first to spot the exploits.

If you’re an All in One SEO Pack plugin user and don’t update, the best case scenario could be finding yourself removed from Google’s search index for spamming. And because a malicious user could change the title, description, and keyword meta tags, it opens up websites to having that information changed by unauthorized third parties.

However, another exploit is much more dangerous for website owners:

we also discovered this bug can be used with another vulnerability to execute malicious Javascript code on an administrator’s control panel. Now, this means that an attacker could potentially inject any javascript code and do things like changing the admin’s account password to leaving some backdoor in your website’s files in order to conduct even more “evil” activities later.

The WordPress plugin has more than 18 million downloads, which means a large number of WordPress-based websites are potentially vulnerable, especially if webmasters don’t take advantage of automatic updates.

Along with WordPress SEO by Yoast, the All in One SEO Pack is one of the most popular WordPress SEO plugins.

As yet, the plugin’s creator hasn’t made any comment about the situation on his Twitter account or websites.