Read the excerpt from The Code Book.Other attacks include the use of viruses and Trojan horses. Eve might design a virus that infects PGP software and sits quietly inside Alice's computer. When Alice uses her private key to decrypt a message, the virus would wake up and make a note of it. The next time that Alice connects to the Internet, the virus would surreptitiously send the private key to Eve, thereby allowing her to decipher all subsequent messages sent to Alice.