defined by CIPA. As will appear, we credit the testimony of
plaintiffs' expert Dr. Geoffrey Nunberg that the blocking
software is (at least for the foreseeable future) incapable of
effectively blocking the majority of materials in the categories
defined by CIPA without overblocking a substantial amount of
materials. Nunberg's analysis was supported by extensive record
evidence. As noted above, this inability to prevent both
substantial amounts of underblocking and overblocking stems from
several sources, including limitations on the technology that
software filtering companies use to gather and review Web pages,
limitations on resources for human review of Web pages, and the
necessary error that results from human review processes.


Because the filtering software mandated by CIPA will block
access to substantial amounts of constitutionally protected
speech whose suppression serves no legitimate government
interest, we are persuaded that a public library's use of
software filters is not narrowly tailored to further any of these
interests. Moreover, less restrictive alternatives exist that
further the government's legitimate interest in preventing the
dissemination of obscenity, child pornography, and material
harmful to minors, and in preventing patrons from being
unwillingly exposed to patently offensive, sexually explicit
content. To prevent patrons from accessing visual depictions
that are obscene and child pornography, public libraries may
enforce Internet use policies that make clear to patrons that the
library's Internet terminals may not be used to access illegal
speech. Libraries may then impose penalties on patrons who
violate these policies, ranging from a warning to notification of