You can enter a personal passphrase here. This lets us identify you as the original uploader of the file so that noone else but you can replace the file. You do not have to register as a user to use a passphrase. Just write anything you want when you upload. The next time you want to replace your file state the same passphrase and the admin will know that you are the original uploader. The passphrase can be left empty if you wish. Though this means that there's no way for the adminstrators to identify the uploader of your file. When replacing a file it makes it easier for the administrators if you use the file replace function on your file readme page. You can write anything as a passphrase, such as: "The cat ate my hamster" "My favourite color is blue" (These are just examples, refrain from copying these examples for your file for security reasons.)