About 1 percent of Web sites indexed by Google and Microsoft are sexually explicit, according to a U.S. government-commissioned study.
Government lawyers introduced the study in court this month as the Justice Department seeks to revive the 1998 Child Online Protection Act, which required commercial Web sites to collect a credit card number or other proof of age before allowing Internet users to view material deemed "harmful to minors."
The U.S. Supreme Court blocked the law in 2004, ruling it also would cramp the free speech rights of adults to see and buy what they want on the Internet. The court said technology such as filtering software may work better than such laws.
The American Civil Liberties Union, which challenged the law on behalf of a broad range of Web publishers, said the study supports its argument that filters work well.
The study concludes that the strictest filter tested, AOL's Mature Teen, blocked 91 percent of the sexually explicit Web sites in indexes maintained by Google Inc. and Microsoft Corp.'s MSN.
Filters with less restrictive settings blocked at least 40 percent of sexually explicit sites, according to the study of random Web sites by Philip B. Stark, a statistics professor at University of California, Berkeley.
"Filters are more than 90 percent effective, according to Stark," ACLU attorney Chris Hansen said Tuesday during a break in the trial. "Also, with filters, it's up to the parents how to use it, whereas COPA requires a one-solution-fits-all (approach)."
COPA follows Congress' unsuccessful 1996 effort to ban online pornography. The Supreme Court in 1997 deemed key portions of that law unconstitutional because it was too vague and trampled on adults' rights. It would have criminalized putting adult-oriented material online where children can find it.
The 1998 law narrowed the restrictions to commercial Web sites and defined indecency more specifically.
In 2000, Congress also passed a law requiring schools and libraries to block porn using software filters if they receive certain federal funds. The high court upheld that law in 2003.
Justice Department lawyers Theodore Hirt and Raphael Gomez declined to comment Tuesday on Stark's findings.
Stark prepared the report based on information the Justice Department obtained through subpoenas sent to search engine companies and Internet service providers.
Google refused one such subpoena for 1 million sample queries and 1 million Web addresses in its database, citing trade secrets. A judge limited the amount of information the company had to provide.
Stark also examined a random sample of search-engine queries. He estimated that 1.7 percent of search results at Time Warner Inc.'s AOL, MSN and Yahoo Inc. are sexually explicit and 1.1 percent of Web sites cataloged at Google and MSN fall in that category.
About 6 percent of searches yield at least one explicit Web site, he said, and the most popular queries return a sexually explicit site nearly 40 percent of the time.
But filters blocked 87 percent to 98 percent of the explicit results from the most popular searches on the Web, Stark found.
Stark also said that about half the sexually explicit Web sites found in the Google and MSN indexes are foreign, making them beyond the reach of U.S. law. But he agreed with government assertions that the most popular sites are domestic.
"COPA — right out of the bat — doesn't block the 50 percent (posted) overseas," Hansen said. "So COPA is substantially less than 50 percent effective."
Closing arguments in the four-week, non-jury trial before Senior U.S. District Judge Lowell Reed Jr. are expected Monday.
The law, signed by then-President Clinton, requires Web sites to get credit card information or some other proof of age from adults who want to view material that may be considered harmful to children. It would impose a $50,000 fine and six-month prison term on commercial Web site operators that allow minors to view such content, which is to be defined by "contemporary community standards."
The law has yet to be enforced. The U.S. Supreme Court upheld a preliminary injunction, ruling in June 2004 that the plaintiffs were likely to prevail.
The plaintiffs, including Salon.com, say they would fear prosecution under the law for publishing material as varied as erotic literature to photos of naked inmates at Iraq's Abu Ghraib prison.