The Internet maintains a significant part of American adult entertainment, also because the 1997 "Reno v. American Civil Liberties Union" case specified that the term "" has no specific legal meaning in the context of the Internet. More recent federal efforts, such as the CAN-SPAM Act of 2003 expressly addressed the Internet. On May 1, 2000, American Express announced it would no longer cover transactions from adult sites. According to the committee to Study Tools and Strategies for Protecting Kids from Pornography and Their Applicability to Other Inappropriate Internet Content, there are over 100,000 subscription sites with adult content in the United States, with each site having multiple web pages. On average, a paid subscription generates $20 to $40 per month in revenue, however, an in-depth analysis is complicated. If a visitor site connects to a pay site and signs up for content, it receives a conversion fee from the larger site. A successful large operation is often an umbrella company serving many markets with pay sites. Around this core and its affiliates is a system of ad-supported service sites. The so-called portable porn market is in its initial stage in the U.S.