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1、天津职业技术师范大学2014界本科生毕业设计天津职业技术师范大学毕业设计——外文科技文献翻译专业：计算机科学与技术班级学号：0914–12学生姓名：刘海玲指导教师：郭燕莎讲师二○一四年六月天津职业技术师范大学2014界本科生毕业设计COMPUTERVIRUSESWhatarecomputerviruses?AccordingtoFredCohen’swell-knowndefinition,acomputervirusisacomputerprogramthatcaninfectothercomputerprogramsbymodifyingtheminsuchaway
2、astoincludea(possiblyevolved)copyofitself.Notethataprogramdoesnothavetoperformoutrightdamage(suchasdeletingorcorruptingfiles)inordertobecalleda“virus”.However,Cohenusesthetermswithinhisdefinition(e.g.“program”and“modify”)abitdifferentlyfromthewaymostanti-virusresearchersusethem,andclassi
3、fiesasvirusessomethingswhichmostofuswouldnotconsiderviruses.Computervirusesarebitsofcodethatdamageoreraseinformation,files,orsoftwareprogramsinyourcomputer,muchlikevirusesthatinfecthumans,computervirusescanspread,andyourcomputercancatchaviruswhenyoudownloadaninfectedfilefromtheInternetor
4、copyaninfectedfilefromadiskette.Oncethevirusesisembeddedintoyourcomputer’sfiles,itcanimmediatelystarttodamageordestroyinformation,oritcanwaitforaparticulardateoreventtotriggeritsactivity.Whatarethemaintypesofviruses?Generally,therearetwomainclassesofviruses.Thefirstclassconsistsofthefile
5、Infectorswhichattachthemselvestoordinaryprogramfiles.Theseusuallyinfectarbitrary.COMand/or.EXEprograms,thoughsomecaninfectanyprogramforwhichexecutionisrequested,suchas.SYS,.OVL,.PRG,&.MNUfiles.Fileinfectorscanbeeitherdirectactionorresident.Adirect-actionvirusselectsoneormoreotherprograms
6、toinfecteachothertimetheprogramwhichcontainsitisexecuted,andthereafterinfectsotherprogramswhen“they”areexecuted(asinthecaseoftheJerusalem)orwhencertainotherconditionsarefulfilled.TheViennaisanexampleofadirect-actionvirus.Mostothervirusesareresident.Thesecondclassissystemorboot-recordinfe
7、ctors:thoseviruses,whichinfectexecutablecode,foundincertainsystemareasonadiskthatarenotordinaryfiles.OnDOSsystems,thereareordinaryboot-sectorviruses,whichinfectonlytheDOSboot天津职业技术师范大学2014界本科生毕业设计sectorondiskettes.ExamplesincludeBrain,Stoned,Empire,Azusa,andMichelangelo.S
