But according to the U.S. Justice Department, Web filters are not enough to protect minors. The agency voiced its concern about the technology last week as it geared up to defend an antiporn law that's under attack from civil liberties advocates.
The case, which deals with the 1998 Child Online Protection Act,Thursday after the department subpoenaed Internet search companies, including Google and Yahoo, for millions of search records.
Prosecutors said they need the records to understand the behavior of Web users and how frequently they encounter pornography. Internet addresses obtained from the search engines could be tested against filtering programs to evaluate their effectiveness, the agency said in a court filing.
Casting doubt on the usefulness of Web filters should put American families on edge. More than half of U.S. families with online teens use filtering programs, with more than 12 million copies of such software in use, according to a study conducted last year by the Pew Internet and American Life Project. The report indicated that use of filters in U.S. homes grew 65 percent from four years earlier, as children logged on to the Web in ever greater numbers and the online porn industry continued to flourish.
So just how well do such tools really work? Experts say the technology is not flawless but that it's become more sophisticated in recent years. For instance, developers of filters have learned to thwart some of the more common devices designed to disable them and have added more customization features that give parents greater control over the type of material that can be blocked.
"They're not perfect, and it's hard to see how they ever really would be," said Amanda Lenhardt, a researcher at the Pew Internet and American Life Project. "But they are relatively effective. They do a reasonably good job."
The Consumers Union, which publishes Consumer Reports, agrees. The company re-evaluated 11 products in June, concluding that filtering software has improved since a previous report in 2001 but that the products are "still fallible."
"Filters keep most, but not all, porn out," the group writes in an online overview of the report.
The products that scored highest in the Consumers Union's evaluation were Safe Eyes from SafeBrowse.com, Microsoft's Parental Controls, CyberPatrol from SurfControl, Symantec's Norton Internet Security and McAfee's Privacy Service. Most took just minutes to set up, the group said.
"We've come a long way from the days when searching on 'Little Bo Peep' would yield adult sites for the first 20 listings," said Ray Everett Church, a privacy consultant at PrivacyClue, a research firm.
Web filtering software blocks access to objectionable material through a variety of methods, including blacklists, keyword lists, content rating systems and white lists. Blacklists consist of a predetermined set of Web addresses and will not let users visit specific Web pages.
A keyword list actually scans Web sites for undesirable text and, in some cases, images. If it finds a match, the browser refuses to render the site or pops up a warning. White lists, considered the most restrictive method, block access to all sites except those selected by the filter company. Some filters also work in conjunction with Web site ratings, a voluntary system that relies on Web developers providing an honest description of their content.
Some Internet service providers, including AOL, also try to do their part. Twenty-five percent of AOL's 20 million members sign on under parentally controlled screen names.
"It is a robust and multileveled set of controls to help ensure kids don't have access to inappropriate content and do have access to useful and appropriate content," said AOL spokesman Andrew Weinstein.
As advanced as some of these programs have become, Internet