A U.S. appeals court has for the third time struck down a law intended to keep Web sites with sexually oriented themes away from children, with judges saying the law is a vague and overly broad attack on free speech.

The U.S. Court of Appeals for the 3rd Circuit, in a ruling released Tuesday, struck down the Child Online Protection Act (COPA), a law passed by Congress in 1998. COPA required that all Web sites containing "material harmful to minors," including pictures, recordings and writing, restrict access based on age.

COPA defined material harmful to minors as something the "average person, applying contemporary community standards, would find ... is designed to appeal to, or is designed to pander to, the prurient interest." People who posted adult content without blocking minors' access could face up to six months in prison under the law.

COPA appears to violate the First Amendment of the U.S. Constitution protecting free speech, and the U.S. government hasn't made its case that the law is necessary, 3rd Circuit judges wrote. "COPA criminalizes a category of speech -- 'harmful to minors' material -- that is constitutionally protected for adults," the judges wrote.

Opponents of the law, including the American Civil Liberties Union (ACLU), the Electronic Frontier Foundation, Nerve.com, Salon.com, the Urban Dictionary and the Sexual Health Network, argued the law amounted to government censorship and was so broad that it would affect many Web sites, including those that included information on sexually transmitted diseases.

"For years the government has been trying to thwart freedom of speech on the Internet, and for years the courts have been finding the attempts unconstitutional," Chris Hansen, senior staff attorney with the ACLU First Amendment Working Group, said in a statement. "The government has no more right to censor the Internet than it does books and magazines."

Opponents of COPA have successfully challenged it in court several times. In 2000, the 3rd Circuit upheld a lower court's injunction against the implementation of the law, and in 2002, the U.S. Supreme Court upheld the injunction but sent the law back to U.S. district court. In 2003, the 3rd Circuit ruled that the law violated the U.S. Constitution.

The IDG News Service is a Network World affiliate.