The techniques developed to protect single computers and network-linked computer systems
from accidental or intentional harm are called computer security. Such harm includes destruction
of computer hardware and software, physical loss of data, and the deliberate invasion of
databases by unauthorized individuals.
Data may be protected by such basic methods as locking up terminals and replicating data in
other storage facilities. Most sophisticated methods include limiting data access by requiring the
user to have an encoded card or to supply an identification number or password. Such procedures
can apply to the computer-data system as whole or may be pinpointed for particular information
banks or programs. Data are frequently ranked in computer files according to degree of
confidentiality.
Operating systems and programs may also incorporate built-in safeguards, and data may be
encoded in various ways to prevent unauthorized persons from interpreting or even copying the
material. The encoding system most widely user in the United States is the Data Encryption
Standard (DES) designed by IBM and approved for use by the National Institute of that are then
repeated several times. Very large-scale computer systems, for example, the U.S. military's
Advanced Research Project Agency Network (ARPANET), may be broken up into smaller
subsystems for security purposes, but smaller system in government and industry are more prone to
system-wide invasions. At the level of personal computers, security possibilities are fairly minimal.
Most invasions of computer systems are for international or corporate spying or sabotage,
but computer hackers may take the penetration of protected databanks as a challenge, often with

no object in mind other than accomplishing a technological feat. Of growing concern is the
deliberate implantation in computer programs of worms or viruses that, if undetected, may
progressively destroy databases and other software. Such infected programs have appeared in the
electronic bulletin boards available to computer users. Other viruses have been incorporated into
computer software sold commercially. No real protection is available against such bugs except
the vigilance of manufacturer and user.

1, invasion  [in'veiʒən]
n. 入侵，侵略；侵袭；侵犯

2, sophisticated  [sə'fistikeitid]
adj. 复杂的；精致的；久经世故的；富有经验的
v. 使变得世故；使迷惑；篡改（sophisticate的过去分词形式）
3, pinpointed 
v. 指出正确的位置；准确地找到（pinpoint的过去分词）
4, sabotage  ['sæbətɑ:ʒ, ,sæbə'tɑ:ʒ]
vt. 妨害；对…采取破坏行动
vi. 从事破坏活动
n. 破坏；破坏活动；怠工
5, penetration  [,peni'treiʃən]
n. 渗透；突破；侵入；洞察力
6, implantation  [,implɑ:n'teiʃən, -plæn-]
n. 移植；灌输；鼓吹
7, vigilance  ['vidʒiləns]
n. 警戒，警觉；警醒症