SafeNote is a free web-based service which allows you to share a note or a file with confidentiality. There is no way to spying on you even to a hacker.
Sender just has to create a note or upload a file and system will automatically generate a secure link for them. Then they can send it to the relevant recipient. As soon as receiver read the note or download the file, the system will automatically destroy the note/file. There is no way to recover it, even to the same person.