In general, filtering software works in one of three ways:

1. First, filtering software can block key words, including those deemed sexual, hateful, violent or slang. Examples include breast, sex, nigger, lynching and cock.

2. Second, filtering software can block specific web sites in one of two ways. Either the software blocks everything except specific web sites, referred to as an "allow list," or the software blocks everything except a list of sites deemed unacceptable by the software manufacturer, referred to as a "denial list."

3. Finally, filtering software can block by protocol, that is, by portions of the Internet. For example, librarians could block chat rooms, news groups and e-mail.

Opposing Viewpoints

According to those who oppose filtering software in libraries, filters are perfectly appropriate at home because parents select the company that determines the content their children access on the Internet and that decision only affects the family. However, critics such as the American Library Association have argued that the use of filtering software in public libraries results in librarians not knowing what or how content is filtered since software is proprietary information. Even though the secrecy may be an economic necessity, the process of making decisions without adequate information seems to be in opposition to the role of a librarian.

Supporters of library filters, however, have argued that using such filters is analogous to choosing not to acquire material, something that librarians face every day due to limited budgets and shelf space. In addition, since librarians already allow outside vendors to choose other materials, such as CD-ROMS and books bought on an approval plan, retired librarian David Bruce and other filtering proponents have said that using filtering software vendors is no different than using book and CD vendors.

Filtering software can give parents and the government a false sense of security, however. Even if government-mandated filtering software is installed in public libraries, patrons still could be exposed to sexually explicit material and other material deemed "harmful."

• For example, key word blocking software only searches text and not graphics. Thus, sexually-explicit photos still could be accessed.

• In addition, list-based filtering, where specific web site addresses are blocked, is not foolproof since hundreds, if not thousands, of new web sites are added hourly.

• Also, it is technically impossible for human beings employed by filtering software companies, such as Cyber Patrol and SurfWatch, to prescreen millions of Internet sites.

Since no program can process context, filtering software cannot distinguish between constitutionally-protected speech, such as literature, and speech which receives no First Amendment protection, such as obscenity. This inability to make such an important distinction is a simple human truth, rather than a design flaw, and therefore, it is unlikely to be remediable in the future, according to the American Civil Liberties Union.