Disable external links already posted or prevent SEO from finding external links

[PracticalBot]

We run a very big board with over 4 millions posts and we have an issue with spam related SEO because of the big amount of external links we have. Is there away to remove or disable external links or preferably prevent search engines bots from seeing/indexing external links. If there is a way to remove external links, how can we exclude external images?

برای دیدن لینک ها باید ثبت نام کنید