Browsing behavior exposes identities on the Web

How easy is it to uniquely identify a person based solely on their web browsing behavior? Here we show that when people navigate the Web, their online browsing traces produce fingerprints that identify them. Merely the four most visited web domains are enough to identify 95% of the individuals. These behavioral fingerprints are stable enough to enable high short-term re-identifiability: we demonstrate that we can re-identify 80% of the individuals in contiguous time slices of data. Our results thus show that what is perhaps the most basic feature of our online habits-namely, which sites we visit most often-is highly unique. Such a privacy threat persists even with limited information about individuals' browsing behavior, reinforcing existing concerns around online privacy.