Political Filtering: Filtering of sites devoted to political opposition, religious freedom, or human-rights issues (top map). Social Filtering: Filtering of sites related to sex, gambling, or drugs, in some cases by institutions such as libraries (bottom map). See mulitmedia link below for larger image with color index. Credit: Bryan Christie

Internet filtering around the world has grown in scale, scope, and sophistication in recent years. These maps (see multimedia box at left), based on a study by an academic consortium, describe the extent to which nations block or restrict online content ranging from political dissent to porn. "Over the course of five years, we've gone from just a few places doing state-based technical filtering ... to more than two dozen," says John Palfrey, executive director of the Berkman Center for Internet and Society at Harvard Law School.

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