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Fun fact: TEMPEST is the reason that asterisks are substituted for passwords onscreen.

Not simply because people can look over your shoulder?

Light is a TEMPEST emission :) It too is EM.

But yeah, you're right. Shoulder surfers are very much why * are used.

Asterisks for passwords predate TEMPEST by many years.

That would be surprising, since Tempest dates from the early 1950's.