to use these techniques, due to the overblocking errors they
introduce, if a filtering company does not use such techniques,
its filter will be ineffective at blocking access to speech that
falls within its category definitions.
Thus, while it would be easy to design, for example, a
filter that blocks only ten Web sites, all of which are either
obscene, child pornography, or harmful to minors, and therefore
completely avoids overblocking, such a filter clearly would not
comply with CIPA, since it would fail to offer any meaningful
protection against the hundreds of thousands of Web sites
containing speech in these categories. As detailed in our
findings of fact, any filter that blocks enough speech to protect
against access to visual depictions that are obscene, child
pornography, and harmful to minors, will necessarily overblock
substantial amounts of speech that does not fall within these
categories.


This finding is supported by the government's failure to
produce evidence of any filtering technology that avoids
overblocking a substantial amount of protected speech. Where, as
here, strict scrutiny applies to a content-based restriction on
speech, the burden rests with the government to show that the
restriction is narrowly tailored to serve a compelling government
interest. See Playboy, 529 U.S. at 816 ("When the Government
restricts speech, the Government bears the burden of proving the
constitutionality of its actions."); see also R.A.V. v. City of
St. Paul, 505 U.S. 377, 382 (1992) ("Content-based regulations
are presumptively invalid."). Thus, it is the government's
burden, in this case, to show the existence of a filtering