In addition, the appeals court took aim at several filtering schemes. Blocking all files of a certain type (such as RAR files) was deemed inappropriate, since a file type has no bearing on the legality of an upload. Scanning by IP address was also tossed, because numerous people can use a single IP address. File name filtering tells you nothing about the contents of a file, so that was tossed. Even content scanning was problematic, as the court noted that this would just lead to encrypted files. Besides, even if you could know that a file was copyrighted, it could still be a legal "private backup" not distributed to anyone else.
Courts making rulings based on actual technical knowledge? What's this world coming to? I note that they even listened to me (okay, probably just other people with similar technical knowledge) and realized that content scanning would be ineffective as it would just lead to ubiquitous encryption with no actual reduction in infringement.