Yahoo has announced New Guidelines for Questionable Products in a post at yahoo search marketing blog.

There are some more categories like Cigarettes, Essay-Writing Services, Fake IDs and Fake Diplomas have been added to unacceptable content.

According to the post-

"As you may already know, we don’t accept ads for certain types of content. Recently, we have added a few categories of unacceptable content to our guidelines. They include:

Cigarettes—Sure, James Dean looks cool smoking in that “Rebel Without A Cause” movie poster, but in our search listings we will not accept ads that sell, facilitate the sale, or promote the sale of cigarettes.
Essay-Writing Services—School is hard, writing papers is a drag, but going through life never learning a thing is even more painful. We no longer accept ads that promote academic paper-writing services and the sale of pre-written essays, theses and dissertations.

Fake IDs and Fake Diplomas—These days lots of things can be fake—nails, lips, other body parts…. But we have to draw the line at fake IDs or credentials. For that reason, we will not accept ads that offer fake IDs, diplomas or educational transcripts.

Firearms, Ammunition and Fireworks—Go blow ‘em up and shoot ‘em up somewhere else, because we will not accept ads that offer or promote the sale of fireworks, firearms or integral parts for these weapons"

Here in more detail-
[link]