WordPress.com has been running advertising on our free hosted blogs since 2006. Many bloggers do not know this because despite the fact they ticked the box required to get a free blog, they did not read the ToS. Many also do not read features page, or advertising entry in the support documents after registering their username and blog(s). Also note that as the ads do not display to us when we are logged in, and as many use browsers with ad blockers when logged out, they may not realize they are there at all. The only way to get rid of all advertising on our free hosted WordPress.com blogs is to purchase an annually renewable No-Ads upgrade.
If you feel an ad is inappropriate please take a screenshot of it and send it to Staff by emailing firstname.lastname@example.org or upload it into your Media Library and contact Staff and let them know it's there for them to view.
Blogger initated advertising is not allowed at WordPress.com. There is an advertising program called WordAds. It’s for well established blogs on their own domains, with suitable content and 20,000 - 25,000 page views or more monthly.