lake Ad blocking or removal on Yahoo pages?

It seems like no matter where I go on Yahoo (the homepages, my e-mail Inbox, etc...), I keep finding obscene ads (not pop-up ads, but ads right on the page, ads for male enhancement, e.g. Naturomax). On advice that it might be a trojan virus causing these ads, I removed all viruses using Avast, but the ads are still there. Is there any way I can block these obscene ads, or better yet, remove them?there