Read-Once Messages?

[Lyle_Seaman at transarc.com]

lefty at apple.com (Lefty) writes:
> Has there been any work done on messages that can be read a single time,
> preferably only by a designated recipient, and is not amenable to being
> captured as it is "played"?  I know that Gibson's poem _Agrippa_ had some
> sort of self-destruct feature built into it, but I don't know what
> mechanism was used to implement this.

I think I received one of these once, but I can't remember what it was.