The Computer Fraud and Abuse Act (CFAA) is a creaking, 1986-vintage US anti-hacking law. It makes it a felony to "exceed authorized access" on a computer you don't own, and some federal prosecutors (including Carmen Ortiz, who prosecuted Aaron Swartz) claim that this means that any time you violate the terms of service on website, that you commit a felony and can be imprisoned.
The Electronic Frontier Foundation has published detailed, user-friendly documentation for the CFAA, including the relevant case-law. It's a must-read for anyone who cares about justice in the 21st century. We click through dozens of impossible terms-of-service every day, and if violating them is a felony, we'll all vulnerable to threats of a long sentence.
The Computer Fraud and Abuse Act (“CFAA”), 18 U.S.C. § 1030, is an amendment made in 1986 to the Counterfeit Access Device and Abuse Act that was passed in 1984 and essentially states that, whoever intentionally accesses a computer without authorization or exceeds authorized access, and thereby obtains information from any protected computer if the conduct involved an interstate or foreign communication shall be punished under the Act. In 1996 the CFAA was, again, broadened by an amendment that replaced the term “federal interest computer” with the term “protected computer.”18 U.S.C. § 1030. While the CFAA is primarily a criminal law intended to reduce the instances of malicious interferences with computer systems and to address federal computer offenses, an amendment in 1994 allows civil actions to brought under the statute, as well.