In Short: Google bought DoubleClick a while ago, an internet-based advertising firm. Today Google launched that program, and it tracks you through cookies.

Privacy aware surfers delete their cookies once in a while, and/or are careful which cookies are stored on their computer. But that won't stop Google from tracking your surfing habits. So if you really want to stop Google from doing that to you, install this 'Advertising Cookie Opt-Out Plug-in'.

Thanks for this. I downloaded the plugin