When hackers compromise a blog, they can create spammy posts there. If the blog is quite busy and spammers specify old dates for their posts, they will not be easy to find them for sites owners and even regular site visitors. Such pages will mostly be seen to search engines, which is the goal of the attack.
Affecting: Any site with a blog.
Cleanup: Identify and remove all spammy posts. Remove all unknown users. Change passwords of all users who can post permissions. Update your CSM.