It is time for a little warning of which might be a new or a very old issue. I recently received a comment to my latest post here on LJ and while it looks only out of place and unrelated (like somebody posting in the wrong thread) it actually contained lots of links to various sites in a hidden "div" section. I didn't dare follow any of them :)
While this is no immediate danger to the journal owner or followers, their pages will show up on search engines as being linked to those other pages. I recommend to use plain text comment notification as it will show any hidden html as well.
Comment is screened and reported. Let's see how this turns out.