I don't know what I did or If I did it but Sourcetree has suddenly started tracking thumbs.db files in all my repositories. I don't know if Windows was not generating thumbs.db previously or sourcetree was never tracking them, but this time, they're everywhere.
It's not possible to remove all of them individually because every folder has it and gitignore will only work for repositories created in the future. What do I do about the old repositories?