We examine the privacy diffusion on the Internet, hidden transactions, and the potential for a few sites to be able to construct a pro-file of individual users. We define and generate a privacy footprint allowing us to assess and compare the diffusion ofprivacy information across a wide variety of sites. We ex-amine the effectiveness of existing and new techniques to reduce this diffusion. Our results show that the size of the privacy footprint is a legitimate cause for concern across thesets of sites that we study.
