If you're running Disqus on your blog, better check your "normal" comment database. All the spam you've deleted in Disqus is there safely in the DB :(
Disqus leaves SPAM comments in the WP DB and secretly displays the spam on the pages (page source).
If a comment is marked as spam or deleted in Disqus, the comment is not removed / marked as spam in the WordPress Db. Big problem if someone stops using Disqus.
And to make things worse, Disqus outputs ALL the spam comments into the page source. They're not visible on the page, but they are in the source. I call that black hat, and that's not cool.
I tested it, verified it and Disqus confirmed the bug, promising solution on the next version: