Here's what we believe happened: CBS requested user data from Last.fm, including user name and IP address. CBS wanted the data to comply with a RIAA request but told Last.fm the data was going to be used for "internal use only." It was only after the data was sent to CBS that Last.fm discovered the real reason for the request. Last.fm staffers were outraged, say our sources, but the data had already been sent to the RIAA.
Interesting Tool to discover whether musical content is RIAA produced or not, so that it can be avoided. (probably affiliated with the boycottRIAA project)