A federal judge on Thursday threw out a 1998 law that makes it a crime for commercial Web site operators to let children access "harmful" material.
In the ruling, the judge said parents can protect their children through software filters and other less restrictive means that do not limit the rights of adults to free speech.
"Perhaps we do the minors of this country harm if First Amendment protections, which they will with age inherit fully, are chipped away in the name of their protection," wrote Senior U.S. District Judge Lowell Reed Jr., who presided over a four-week trial last fall.
The law would have criminalized Web sites that allow children to access material deemed "harmful to minors" by "contemporary community standards." The sites would have been expected to require a credit card number or other proof of age. Penalties included a $50,000 fine and up to six months in prison.
Sexual health sites, the online magazine Salon.com and other Web sites backed by the American Civil Liberties Union challenged the law. They argued that the Child Online Protection Act was unconstitutionally vague and would have had a chilling effect on speech.
The U.S. Supreme Court upheld a temporary injunction in 2004 on grounds the law was likely to be struck down and was perhaps outdated.
Technology experts said parents now have more serious concerns than Web sites with pornography. For instance, the threat of online predators has caused worries among parents whose children use social-networking sites such as News Corp.'s MySpace.
The case sparked a legal firestorm last year when Google challenged a Justice Department subpoena seeking information on what people search for online. Government lawyers had asked Google to turn over 1 million random Web addresses and a week's worth of Google search queries.
A judge sharply limited the scope of the subpoena, which Google had fought on trade secret, not privacy, grounds.