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 experts say they work best when combined with involved parenting. That means parents should talk to children about their online activities, set limits and check up on them.
Choosing a filter that won't falter
Here are some tips from ConsumerReports.org.
Consider your Internet provider. Filtering comes free with AOL, EarthLink or MSN. AOL and MSN both filtered effectively, but AOL blocked sites such as NewsMax, a conservative political site, and Operation Truth, an advocacy site for Iraq War veterans. In both cases, a parent could override the block.
Weigh protection versus interference. All filtering programs either overblock or underblock. For young children, look for maximum protection. For older children, look for filtering software that doesn't overly interfere.
Consider which activities to control. Older children are more likely to engage in activities such as e-mail, instant messaging and gaming. Time-management controls help minimize fighting for the computer.
Decide how much customization you need. If your children aren't close in age, consider a program that can be customized by age. Those that offer more filtering flexibility make fine-tuning easier but may not offer the best protection.
Whichever filter you choose, give your children clear directions on how, when and where they can access the Internet.
"They're not a substitute for parenting," said Danielle Yates, a spokeswoman for the Internet Education Foundation, publisher of GetNetWise.com, an online guide to Internet safety for children and teens. "They're there to help parents when parents can't always be around, but they can't take parents' place. Parents really need to be involved."
To be sure, circumventing filters is not rocket science. Teens can find work-arounds through a simple Google search, which can turn up detailed instructions and pointers for sidestepping filters.
For instance, a Google search for "NetNanny hack" yields a result for Cexx.org, "How to Disable Internet Filtering Programs." NetNanny, made by Anonymizer, is a popular brand of filter.
Proxy sites are another tool for thwarting filters. Browser proxies, such as IPZap.com and IBYPass.org, let people type in an address, and then they redirect all responses from the blocked domain through the proxy's domain. Many filtering companies have wised up to proxy sites and now block access to those sites too. For example, CyberPatrol, which is owned by SurfControl, will categorize browser proxy sites and prevent children from accessing them.
Bennett Haselton, a programmer in Seattle, is one of the many free speech activists in a kind of cat-and-mouse game with filtering companies. Through his site, Peacefire.org, he distributes a free download that lets Web users turn their desktop computers into Web proxies that fly under the radar of filter programs. Users can invite friends with computers protected by filters to use their machines to override the protections.
He launched the program, which takes just minutes to set up, more than two years ago and said visitors download about two dozen copies a day. Haselton, who is concerned about Internet censorship in China and elsewhere, believes concerns about children and Internet porn are overblown.
"I never met anyone who was harmed by having unfettered Internet access," he said. "But I've met plenty of people who have been harmed by being overprotected. The real harm is the harm to critical thinking."
Clearly, a determined teen or child can outsmart a Web filter, but most don't want to, said Lenhardt at the Pew Internet and American Life Project.
"Most kids want to be protected," she said. "A lot of exposure to undesirable material is by accident. Most kids don't want to see it, so most aren't going to be trying to circumvent the protections."
Nonetheless, filtering companies have their hands full trying to handle an exploding amount of content, including video, that's circulating online, Lenhardt said. In addition, they're grappling with new kinds of devices that connect people to the Web, like video iPods and Internet-capable cell phones and handhelds. Web filters could also do a better job of ensuring access to benign material, such as health information, exerts say.
Filter companies say they're up for the challenge. Bob Kessinger, director of operations for CyberPatrol, is emphatic that technology is the answer for shielding children from adult material online.
"Many of the adult sites out there, the content is not hosted in this country; it's a global issue," Kessinger said. "I'm not sure legislation is going to have an effect on that."