Put another way, security is as much a matter of proper usage as proper
algorithms and proper code. See http://www.fas.org/irp/eprint/heath.pdf
for a story of how the NSA and the US Navy got that wrong. For that
matter, read Leo Marks' wonderful memoir "Between Silk and Cyanide".
He's telling a story, not trying to teach, but the message is there
nonetheless.
As technologists, of course, it's incumbent on us to design security
systems that help the user understand consequences of actions, and to
help avoid dangerous situations.
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb