Digital Millennium Copyright Act of 1998 is something that every webmaster should know about, especially we bloggers 😉
Here is some words from EFF website.
Congress enacted section 1201 in response to two pressures. Congress was responding to the perceived need to implement obligations imposed on the U.S. by the 1996 World Intellectual Property Or–ganization (WIPO) Copyright Treaty. Section 1201, however, went further than the WIPO treaty required. The details of section 1201, then, were a response not just to U.S. treaty obligations, but also to the concerns of copyright owners that their works would be widely pirated in the networked digital world.
Section 1201 contains two distinct prohibitions: a ban on acts of circumvention, and a ban on the distribution of tools and technologies used for circumvention.
The first prohibition, set out in section 1201(a)(1), prohibits the act of circumventing a technological measure used by copyright owners to control access to their works (“access controls”). So, for example, this provision makes it unlawful to defeat the encryption system used on DVD movies. This ban on acts of circumvention applies even where the purpose for decrypting the movie would otherwise be legitimate. As a result, when Disney’s Tarzan DVD prevents you from fast-forwarding through the commercials that preface the feature presentation, efforts to circumvent this restriction would be unlawful.