In 2009, police and law enforcement agencies discovered close to 22 million public I.P. addresses that were offering pornographic images of children through peer to peer file sharing. Almost 10 million of the I.P. addresses that were involved in file sharing was located in the United States.
It should be noted that many of the addresses were file-sharing only a single image, leading experts to believe that they were downloaded inadvertently. However, other I.P. addresses were offering thousands of pictures.
Source: Emily Bazelon, “The Price of a Stolen Childhood,” New York Times, January 24, 2013.