In what appears not to be the only case of its kind, the RIAA has withdrawn a suit against a Macintosh user who they claimed was using the Kazaa file sharing service to share 2,000 songs. The problem? Kazaa doesn't run on the Mac.
There is much speculation, but no definitive information, on how the "mistake" occurred, but it appears that either the wrong IP address was used in gathering information for the subpoena, or the IP address was in use by somebody else at the time that the scan was done by the RIAA. This type of thing sometimes occurs when ISPs dynamically assign IP addresses to users (which is often the case). For DSL and Cable users, the IP addresses usually stick around until a power outage or some similar event that takes the modem offline, but for dial-up users, a new IP address is retrieved every time that they access the system.