  We study the diffusion of a true and a false message when agents are biased
and able to verify messages. As a recipient of a rumor who verifies it becomes
informed of the truth, a higher rumor prevalence can increase the prevalence of
the truth. We uncover conditions such that this happens and discuss policy
implications. Specifically, a planner aiming to maximize the prevalence of the
truth should allow rumors to circulate if: verification overcomes ignorance of
messages, transmission of information is relatively low, and the planner's
budget to induce verification is neither too low nor too high.
