"Members of a former software cracking group have discovered that audio files created with one of its cracked programs are distributed with each copy of the Windows XP" ... (Read Article)

The files are at @%windir%\Help\Tours\WindowsMediaPlayer\Audio\Wav@ directory of Windows XP. If these files are opened with a HEX editor (or any Text Editor for that matter) the code contains the signature "Deepz0ne", who was a member of former cracking group "Radium".

Via: Tom's Hardware Guide