Mal/SEORed-A is generic detection for malicious web pages designed to redirect the user to another malicious site.
Users are likely to encounter pages blocked as Mal/SEORed-A when clicking on links in search engine results. The page that is blocked is intended to redirect the user to another remote site, where they will be exposed to further malware (for example, scareware).
There is more information about Mal/SEORed-A on the blog articles Blackhat SEO poisoning topping the charts
and Defending against SEO poisoning attacks with Layered Protection