Technological protection measures (TPM) encompass software, devices or other technologies used to block or limit access to a work, or certain actions with respect to the work (e.g., copying). TPMs include such things as encryption, passwords, and access controls.
Section 1201 of Title 17, enacted as part of the Digital Millennium Copyright Act (DMCA), prohibits anyone from circumventing a “technological measure that effectively controls access to a work.” There is no ban on circumventing a technological measure that protects a right of a copyright owner, such as reproduction or distribution, without controlling access to the work. Circumventing a copy control in and of itself, for example, is not prohibited.
Section 1201 also prohibits manufacturing, providing, or trafficking in devices or services primarily designed to circumvent either access controls or rights controls. There are a number of exceptions to these anti-circumvention provisions.