A recent paper compiled by researchers says that many of the top sites are blocking people that are using computers running known Tor exit-node IP addresses.They are reportedly being blocked, or experiencing a slower service.
Anonymous networks such as Tor already face hostile environments that include deanonymisation attacks and blocks from the government as Tor is often blamed by law enforcement agencies for the internet "going dark".
The researchers from from the University of Cambridge, University of California, University College London and International Computer Science Institute compared internet port scans from Tor exit nodes and compared them to control hosts.
After scanning the top 1,000 Alexa website home pages over almost a year of historic HTTP crawls from the Tor network and control hosts and coming up with methodologies to distinguish censorship events from incidental failures such as those caused by packet loss or network outages, and incorporate consideration of the endemic churn in web-accessible services over both time and geographic diversity.
The results were conclusive - about 69 of the sites that the researchers looked at on average block over 10-50 percent of Tor exit nodes.
The paper concluded: “While many websites block Tor to reduce abuse, doing so inadvertently impacts users from censored countries who do not have other ways to access censored internet content. Anonymous communication on the internet is a critical resource for people whose access to the internet is restricted by governments. However, the utility of anonymity networks is threatened by services on the internet that block or degrade requests from anonymous users.”
The researchers also noted that in the future they will “investigate more effective technical and policy-level solutions to mitigate the second-class treatment of anonymous users.”