In June of 1997, Congress voted 94-0 to add an amendment to a Department of Defense spending bill to prohibit the
distribution of bomb-making instructions in the United States. The penalty for violating this law is a fine of $250,000 and/or a
maximum of 20 years imprisonment. Senator Dianne Feinstein (D-California) was the sponsor of the bill. In April of 1997, the Justice Department released a study revealing a connection between the availability of bomb-making
instructions and the making of bombs. Although prohibiting the distribution of bomb-making instructions could be seen as a violation of the First Amendment, the Justice Department decided that the distribution of such materials was an obstruction of justice and not a free-speech right, providing the amendment was narrowly written. Thus, the Feinstein Amendment only precludes the distribution of material intentionally directed toward a "a federal offense or other criminal purpose affecting interstate commerce".
The "criminal purpose" provision is extremely important, since this means you can find information on explosive devices that are intended for entertainment purposes (e.g., fireworks and rocketry) and you can still learn basic concepts of chemistry, which necessarily include information about explosives. It also protects instructors engaged in teaching about bomb-making for the purpose of devising means of disarming them and protecting military and civilian personnel.
I wonder whether the legislation has been effective in deterring would-be terrorists or, more commonly, curious individuals, from making explosive devices or other weapons. Since 1997, has there been a decrease in the number of would-be bombmakers?