Internet filtering has thus become a major public policy issue, and is likely to remain so.
Nearly every one, however, revealed massive over-blocking by filtering software.
This problem stems from the very nature of filtering, which must, because of the sheer number of Internet sites, rely to a large extent on mindless mechanical blocking through identification of key words and phrases.
Even where company employees did review Web sites, there arose massive problems of subjectivity.
The political attitudes of the different filter manufacturers were reflected in blocking decisions, particularly with respect to such subjects as homosexuality, human rights, and criticism of filtering software.
Third-party rating and filtering systems have thus become the industry standard, at least in the United States. erroneously claimed that its "X-Stop" software was able to identify and block only "illegal" obscenity and child pornography: an impossible task, since legal judgments in both categories are subjective, and under the Supreme Court's three-part obscenity test, determinations of legality vary depending on different communities' standards of "prurience" and "patent offensiveness." The late 1990s saw political battles in many communities over the use of filtering products in public libraries.