


We also identify that Tor directories significantly contribute to both communication and information dissemination through the network. The results recover the dark-to-surface network as a single massive, connected component where over 90% of identified Tor hidden services have at least one link to the surface world. This work addresses this gap by a broad evaluation on: (a) the network of links from Tor to the surface Web, (b) the vulnerability of Tor hidden services against the information leakage, (c) the changes in the overall hyperlink structure of Tor hidden services caused by linking to surface websites, and (d) the type of information and services provided by the domains with significant impact on Tor’s network. However, there is still a lack of knowledge about the information leakage attributed to the links from Tor hidden services to the surface Web. The previous research on Tor investigated either the security and privacy concerns or the information and hyperlink structure. Tor is the most well-known anonymity network that protects the identity of both content providers and their clients against any tracking on the Internet. In fact, more than 20% of the onion domains we visited imported resources from the Surface Web, and links to the Surface Web are even more prevalent than to other onion domains.įinally, we measured for the first time the prevalence and the nature of web tracking in Tor hidden services, showing that, albeit not as widespread as in the Surface Web, tracking is notably present also in the Dark Web: more than 40% of the scripts are used for this purpose, with the 70% of them being completely new tracking scripts unknown by existing anti-tracking solutions. Our study also measures for the first time the tight connection that exists between Tor hidden services and the Surface Web. According to our experiments, Tor hidden services are organized in a sparse but highly connected graph, in which around 10% of the onions sites are completely isolated. For each page we analyzed its links, resources, and redirections graphs, as well as the language and category distribution. To fill this gap, we developed a dedicated analysis platform and used it to crawl and analyze over 1.5M URLs hosted in 7257 onion domains. However, while its protocol and relay security have already been extensively studied, to date there is no comprehensive analysis of the structure and privacy of its Web Hidden Service. Tor is a well known and widely used darknet, known for its anonymity.
