Google's 0M Drug Sales Settlement Brought on by Con Artist
Google allegedly allowed Canadian pharmacies to use its AdSense platform to illegally sell prescription drugs to US consumers. Whitaker reportedly posed as an agent for online pharmacies in "dozens of recorded phone calls and e-mail exchanges with …
Read more on PCWorld (blog)

What Does Google Know About You?
Based on this information the company collects, they can then show advertising to you they believe will be relevant (I believe it's on websites that have Adsense enabled). You can opt out of this if you'd like, and I chose to opt out via Chrome plugin.
Read more on Elliot’s Blog (blog)