According to Google: In addition, we may serve ads based on your interests. As you browse websites that have partnered with us or Google sites using the Double

According to Google: In addition, we may serve ads based on your interests. As you browse websites that have partnered with us or Google sites using the DoubleClick cookie, such as YouTube, Google may place the DoubleClick cookie in your browser to understand the types of pages visited or content that you viewed. Based on this information, Google associates your browser with relevant interest categories and uses these categories to show interest-based ads. But you can opt-out of Google's behavioral targeting: http://www.google.com/privacy_ads.html http://www.google.com/privacy_ads.html