Apple’s Safari web browser is configured to block third-party cookies by default. We identified four advertising companies that unexpectedly place trackable cookies in Safari. Google and Vibrant Media intentionally circumvent Safari’s privacy feature. Media Innovation Group and PointRoll serve scripts that appear to be derived from circumvention example code.

In the interest of clearly establishing facts on the ground, this post provides technical analysis of Safari’s cookie blocking feature and the four companies’ practices. It does not address policy or legal issues. (More on that soon.)

Before proceeding further, I want to thank the countless friends and colleagues who provided invaluable feedback on this project. In particular: ★★★★★, whose insights have been vital at every step, and Ashkan Soltani, whose crawling data was instrumental in uncovering PointRoll’s practices and understanding the prevalence of cookie blocking circumvention.

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