So Long, And No Thanks for the Externalities: The Rational Rejection of Security Advice by Users

The failure of users to follow security advice has often

been noted. They chose weak passwords, ignore secu-

rity warnings, and are oblivious to certificates. It is

often suggested that users are hopelessly lazy and un-

motivated on security questions. We argue that users'

rejection of the security advice they receive is entirely

rational from an economic perspective. As with many

activities, online crime generates direct losses and ex-

ternalities. The advice offers to shield them from the

direct costs of attacks, but burdens them with the in-

direct costs, or externalities. Since the direct costs are

generally small relative to the indirect ones, they reject

this bargain. We examine three areas of user educa-

tion: password rules, phishing site identification, and

SSL certificates. In each we find that the advice is com-

plex and growing, but the benefit is largely speculative

or moot. In the cases where we can estimate benefit, it

emerges that the burden of following the security advice

is actually greater than the direct losses caused by the


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