Internet access in Iran is subject to official censorship. Iranian authorities' guidelines for ISPs and users reportedly
warn them to avoid all content seen as being in breach of social and cultural norms.[1] In practice, the filtering of
Iranian ISPs extends to cover political as well as pornographic web sites.[2] In September 2003, the U.S.
International Broadcasting Bureau (IBB) sponsored the launch of a service through Anonymizer, Inc., designed to
allow Iranian Internet users to bypass much of Iran's national filtering regime. Throughout this report we refer to the
service as the "IBB Anonymizer" to emphasize that it is distinct from the general services offered to the public by
Anonymizer, Inc.[3]
In December 2003 and April 2004, we ran a series of tests to gauge the accessibility of sites through the IBB
Anonymizer service. We found that many web sites blocked by Iranian ISPs could be successfully accessed through
the IBB Anonymizer service. However, filters built in to the IBB Anonymizer service, intended to prevent Iranians
from using it to view pornographic sites, also have the unintended consequence of blocking access to numerous
non-pornographic pages and sites. At fault appears to be the IBB Anonymizer's unreleased list of automated
"trigger" keywords applied to domain names before any pages are shown to IBB Anonymizer users. These "trigger"
keywords appear to generate a significant number of false-positive results, resulting in a significant amount of
collateral blocking -- "overblocking" -- of non-pornographic sites. For example, the IBB Anonymizer service blocks
non-pornographic websites dealing with women's health issues because the keyword "breast" is within their domain
names. Likewise blocked is the anchor page for links to the U.S. Department of State's overseas missions --
usembassy.state.gov -- because it contains the trigger keyword "ass." The service also blocks almost any site
containing the word "asian" in the domain. Some of these apparently unintentionally blocked sites are themselves
blocked within Iran, resulting in a situation where sites are effectively doubly blocked --by Iranian ISPs and by the
IBB Anonymizer service.
The IBB and Anonymizer Inc. confirmed in separate e-mail exchanges with ONI researchers that the circumvention
service is explicitly configured to block pornography.[4] They explained that this is intended to conserve available
bandwidth and ensure availability of the service to Iranians who wish to visit non-pornographic sites. Several notable
studies have pointed out the difficulty of implementing keyword-based filtering systems in such a way as to avoid
the unintended consequence of "collaterally blocking" non-pornographic sites. The keyword rules that drive the
filters built in to the IBB Anonymizer service are not publicly known, making independent assessment of those rules
and their implications more difficult. (Staff at Anonymizer, Inc., have declined to publicly disclose keywords or
methods, considering them to be proprietary to the company.)
Further, despite IBB Anonymizer assurances that its Iranian users may surf the Web freely and safely, our testing
suggests that the vast majority of its traffic is exposed to monitoring by Iranian authorities and corresponding local
ISPs. Iranian users may not be aware that their use of the service may identify them to Iranian government
authorities as citizens wishing to view forbidden content, or as supportive of the ideas found within that content.