Earlier this year, Microsoft announced an update to negative keywords in AdCenter. This would make it so that negative keywords loaded at the campaign and ad group levels would be combined to filter ad traffic. Before, negative keywords at the ad group level would override the ones at the campaign level.
Today, that update is live.
"If you have negative keywords applied at both the campaign and ad group levels you may experience lower traffic volume, as the negative keywords you assigned at the campaign level will now be applied in conjunction with the ad group level negatives.," Microsoft says in a blog post. "It is highly recommended if you closely review your campaign-level negatives if you have negative keywords uploaded at both the campaign and ad group levels to make sure you aren’t blocking wanted traffic at the ad group level. There is no change to the 10k negative keyword limits at either the campaign or ad group level."
The company provides the following comparison for how negative keywords used to work, with how they work now. I'm not sure whey they went with such a low quality image, but that's what they posted, so sorry.
The company says you should establish negative keywords in each hierarchy based on category in each hierarchy. You should also apply the common negative keywords at the campaign level, Microsoft says, so they could be shared across the lower ad group. Also, keep monitoring the Negative Conflicts Report.
Earlier this week, Microsoft, Yahoo and AOL started offering each others' display inventory.