In reply to Nathan Corbier.

Nathan, you lead me to think of an interesting question. When a user presses the "Fork" button on GitHub, a complete clone of the repository is created, including both open-source and non-open-source files. An ethical user would immediately remove copyrighted material and commit. However, the copyrighted material would still be present in the original version of fork (Git saves all previous versions). Would the copyright holder be able to enforce a DMCA notice based on the presence of copyrighted material in an older commit?