WordPress.com does not use text enhance or text link ads or pop-up ads or links in comments. If you are seeing those then that's a browser-ad-on issue, or in some cases, it's embedded into free games and/or toolbars downloaded from the internet. See here: Bloggers: Beware of Adware. http://onecoolsitebloggingtips.com/2012/09/14/bloggers-beware-of-adware/

If what you are seeing whenever you save or update a post or page is an automatically added code/script block at the end of posts and pages that you can't delete then see here: Malware Targets Macs and Windows PCs http://onecoolsitebloggingtips.com/2012/10/02/malware-targets-macs-and-windows-pcs/