technology that both blocks enough speech to qualify as a
technology protection measure, for purposes of CIPA, and avoids
overblocking a substantial amount of constitutionally protected
speech.
Here, the government has failed to meet its burden. Indeed,
as discussed in our findings of fact, every technology protection
measure used by the government's library witnesses or analyzed by
the government's expert witnesses blocks access to a substantial
amount of speech that is constitutionally protected with respect
to both adults and minors. In light of the credited testimony of
Dr. Nunberg, and the inherent tradeoff between overblocking and
underblocking, together with the government's failure to offer
evidence of any technology protection measure that avoids
overblocking, we conclude that any technology protection measure
that blocks a sufficient amount of speech to comply with CIPA's
requirement that it "protect[] against access through such
computers to visual depictions that are – (I) obscene; (II) child
pornography; or (III) harmful to minors" will necessarily block
substantial amounts of speech that does not fall within these
categories. CIPA Sec. 1712 (codified at 20 U.S.C. Sec. 9134(f)(1)(A)).
Hence, any public library's use of a software filter required by
CIPA will fail to be narrowly tailored to the government's
compelling interest in preventing the dissemination, through
Internet terminals in public libraries, of visual depictions that
are obscene, child pornography, or harmful to minors.


Where, as here, strict scrutiny applies, the government may
not justify restrictions on constitutionally protected speech on
the ground that such restrictions are necessary in order for the