Vanish was a project to "give users control over the lifetime of personal data stored on the web."
[1] The project proposed to allow a user to enter information to send across the internet, thereby relinquishing control of it.
Instead, it breaks up the decryption key into smaller components that are disseminated across distributed hash tables, or DHTs, via the Internet.
While both the user and recipient may have copies of the original encrypted message, the key used to turn it back into plain text is now gone.
Although this particular instance of the data has become inaccessible, it's important to note that the information can always be saved by other means before expiration (copied or even via screen shots) and published again.