It infects the computer's memory, then files as they are opened. It modifies and corrupts certain types of Flash BIOS, software that initializes and manages relationships and data flow between the system devices, including the hard drive, serial and parallel ports and the keyboard. By overwriting part of the BIOS, CIH can keep a computer from starting up when the power is turned on. Some variants of CIH activate on April 26th or June 26th, while others activate on the 26th of every month. Encryption - science of scrambling text so that no one but the desired parties, sender and receiver, can read the data.
Encryption turns the data into a secret code.
PGP combines two algorithms, RSA and IDEA, to encrypt plaintext. Zimmermann was the subject of a Federal Investigation for exporting his PGP software. Charges were eventually dropped. See more details on encryption by Prof Marchant. See legislation about encryption .