计算机英语：入侵计算机的特点和破坏安全类型

　　（1）In an interruption，an asset of the system becomes lost or unavailable or unusable．An example is malicious destruction of a hardware device，erasure of a program or data file，or failure of on operating system file manager so that it cannot find a particular disk file．
　　（2）An interception means that some unauthorized party has gained access to an asset．The outside party can be a person，a program，or a computing system．Examples of this type of failure are illicit copying of program or data files，or wiretapping to obtain data in a network．While a loss may be discovered fairly quickly，a silent interceptor may leave no traces by which the interception can be readily detected[4]．
　　（3）If an unauthorized party not only accesses but tampers with an asset，the failure becomes a modif ication．For example，someone might modify the values in a database，alter a program so that it performs an additional computation，or modify data being transmitted electronically．It is even possible for hardware to be modified．Some cases of modification can be detected with simple measures，while other more subtle changes may be almost impossible to detect．
    （4）Finally，an unauthorized party might fabricate counterfeit objects for a computing system．The intruder may wish to add spurious transactions to a network communication system，or add records to an existing data base．Sometimes these additions can be detected as forgeries，but if skillfully done，they are virtually indistinguishable from the real thing．
　　These four classes of interference with computer activity—interruption，interception，modification，and fabrication—can describe the kinds of exposures possible．Examples of these kinds of interferences are shown in Fig. 18-2．
    

NOTES
[1]not…，nor结构，译为“既不…也不…”，against which…为定语从句，修饰前面的one，one代表means。
[2]主句中由that引出的是宾语从句。because引出的原因状语从句中，主语为strengthening one，more appealing为宾语补足语。
[3]由分号隔开的长句，后一句有插入语as are natural disasters。
[4]While引出的是让步状语从句，可译为“虽然…”。

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