.SIDD File Extension
File TypeiTunes Authorization Data File
What is a SIDD file?
Data file used by iTunes, a music and video playback application; contains data that authorizes the computer and user to play purchased songs and videos with the user account; similar to .SIDB and .SIDN files; not meant to be opened manually by the user.
In Windows 7 and 8, iTunes stores SIDD files to the following directory:
C:\ProgramData\Apple Computer\iTunes\SC Info\
iTunes for Windows XP uses this location:
C:\Documents and Settings\All Users\Application Data\Apple Computer\iTunes\SC Info\
NOTE: If iTunes doesn't open after you've installed a new version in Windows, you can fix this by deleting the SC Info.sidb, SC Info.sidd, and SC Info.sidn files from the directories listed above. After deletion, restart your computer and then reopen iTunes.