  We propose a new method to protect Over-The-Air (OTA) computation schemes
against passive eavesdropping. Our method uses a friendly jammer whose signal
is -- contrary to common intuition -- stronger at the legitimate receiver than
it is at the eavesdropper. We focus on the computation of arithmetic averages
over an OTA channel. The derived secrecy guarantee translates to a lower bound
on the eavesdropper's mean square error while the question of how to provide
operationally more significant guarantees such as semantic security remains
open for future work. The key ingredients in proving the security guarantees
are a known result on channel resolvability and a generalization of existing
achievability results on coding for compound channels.
