If Eve parks a van outside Alice's house, she can use sensitive tempest equipment to identify each individual keystroke that Alice makes on her computer. This would allow Eve to intercept the message as it is typed into the computer, before it is encrypted. To defend against tempest attacks, companies are already supplying shielding material that can be used to line the walls of a room to prevent the escape of electromagnetic signals.

In this excerpt, the author explains

why computers are easily stolen.
why keyboards are unsanitary.
how computer security can be broken.
how friends share secret messages.