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郑州大学毕业设计——外文科技文献翻译题目：计算机病毒指导教师：李正民职称：副教授学生姓名：张永星学号：20052430239专业：计算机科学与技术院（系）：信息工程学院完成时间：2009年5月25日2009年05月25日郑州大学毕业设计（外文文献翻译）计算机病毒2COMPUTERVIRUSESWhatarecomputerviruses?AccordingtoFredCohen’swell-knowndefinition,acomputervirusisacomputerprogramthatcaninfectothercomputerprogramsbymodifyingtheminsuchawayastoincludea(possiblyevolved)copyofitself.Notethataprogramdoesnothavetoperformoutrightdamage(suchasdeletingorcorruptingfiles)inordertobecalleda“virus”.However,Cohenusesthetermswithinhisdefinition(e.g.“program”and“modify”)abitdifferentlyfromthewaymostanti-virusresearchersusethem,andclassifiesasvirusessomethingswhichmostofuswouldnotconsiderviruses.Computervirusesarebitsofcodethatdamageoreraseinformation,files,orsoftwareprogramsinyourcomputer,muchlikevirusesthatinfecthumans,computervirusescanspread,andyourcomputercancatchaviruswhenyoudownloadaninfectedfilefromtheInternetorcopyaninfectedfilefromadiskette.Oncethevirusesisembeddedintoyourcomputer’sfiles,itcanimmediatelystarttodamageordestroyinformation,oritcanwaitforaparticulardateoreventtotriggeritsactivity.Whatarethemaintypesofviruses?Generally,therearetwomainclassesofviruses.ThefirstclassconsistsofthefileInfectorswhichattachthemselvestoordinaryprogramfiles.Theseusuallyinfectarbitrary.COMand/or.EXEprograms,thoughsomecaninfectanyprogramforwhichexecutionisrequested,suchas.SYS,.OVL,.PRG,&.MNUfiles.Fileinfectorscanbeeitherdirectactionorresident.Adirect-actionvirusselectsoneormoreotherprogramstoinfecteachothertimetheprogramwhichcontainsitisexecuted,andthereafterinfectsotherprogramswhen“they”areexecuted(asinthecaseoftheJerusalem)orwhencertainotherconditionsarefulfilled.TheViennaisanexampleofadirect-actionvirus.Mostothervirusesareresident.Thesecondclassissystemorboot-recordinfectors:thoseviruses,whichinfectexecutablecode,foundincertainsystemareasonadiskthatarenotordinaryfiles.OnDOSsystems,thereareordinaryboot-sectorviruses,whichinfectonlytheDOSboot郑州大学毕业设计（外文文献翻译）计算机病毒3sectorondiskettes.ExamplesincludeBrain,Stoned,Empire,Azusa,andMichelangelo.Suchvirusesarealwaysresidentviruses.Finally,afewvirusesareabletoinfectboth(theTequilavirusisoneexample).Thereareoftencalled“multipartite”viruses,thoughtherehasbeencriticismofthisname;anothernameis“boot-and-file”virus.Filesystemorclusterviruses(e.g.Dir-II)arethosethatmodifydirectorytableentriessothatthevirusisloadedandexecutedbeforethedesiredprogramis.Notethattheprogramitselfisnotphysicallyaltered;onlythedirectoryentryis.Someconsidertheseinfectorstobeathirdcategoryofviruses,whileothersconsiderthemtobeasub-categoryofthefileinfectors.Whataremacroviruses?Manyapplicationsprovidethefunctionalitytocreatemacros.Amacroisaseriesofcommandstoperformsomeapplication-specifictask.Macrosaredesignedtomakelifeeasier,forexample,toperformsomeeverydaytasksliketext-formattingorspreadsheetcalculations.Macroscanbesavedasaseriesofkeystrokes(theapplicationrecordwhatkeysyoupress);ortheycanbewritteninspecialmacrolanguages(usuallybasedonrealprogramminglanguageslikeCandBASIC).Modernapplicationscombinebothapproaches;andtheiradvancedmacrolanguagesareascomplexasgeneralpurposeprogramminglanguages.Whenthemacrolanguageallowsfilestobemodified,itbecomespossibletocreatemacrosthatcopythemselvesfromonefiletoanother.Suchself-replicatingmacrosarecalledmacroviruses.MostmacrovirusesrununderWordforWindows.Sincethisisaverypopularwordprocessor,itprovidesaneffectivemeansforvirusestospread.MostmacrovirusesarewrittenusingthemacrolanguageWordBasic.WordBasicisbasedonthegoodoldBASICprogramminglanguage.However,ithasmany(hundredsof)extensions(forexample,todealwithdocuments:edit,replacestring,obtainthenameofthecurrentdocument,opennewwindow,movecursor,etc.).WhatisaTrojanhorseprogram?Atypeofprogramthatisoftenconfusedwithvirusesisa‘Trojanhorse’program.郑州大学毕业设计（外文文献翻译）计算机病毒4Thisisnotavirus,butsimplyaprogram(oftenharmful)thatpretendstobesomethingelse.Forexample,youmightdownloadwhatyouthinkisanewgame;butwhenyourunit,itdeletesfilesonyourharddrive.Orthethirdtimeyoustartthegame,theprogramE-mailyoursavedpasswordstoanotherperson.Note:simplydownloadafiletoyourcomputerwon’tactivateavirusorTrojanhorse;youhavetoexecutethecodeinthefiletotriggerit.Thiscouldmeanrunningaprogramfile,oropeningaWord/Exceldocumentinaprogram(suchasWordorExcel)thatcanexecuteanymacrosinthedocument.Whatkindoffilescanspreadviruses?Viruseshavethepotentialtoinfectanytypeofexecutablecode,notjustthefilesthatarecommonlycalled“programfiles”.Forexample,somevirusesinfectexecutablecodeinthebootsectoroffloppydiskorinsystemareasofharddrives.Anothertypeofvirus,knownasa“macro”virus,caninfectwordprocessingandspreadsheetdocumentsthatusemacros.Andit’spossibleforHTMLdocumentscontainingJavaScriptorothertypesofexecutablecodetospreadvirusesorothermaliciouscode.Sincevirusescodemustbeexecutedtohaveanyeffect,filesthatthecomputertreatsaspuredataaresafe.Thisincludesgraphicsandsoundfilessuchas.gif,.jpg,.mp3,.wav,.etc.,aswellasplaintextin.txtfiles.Forexample,justviewingpicturefileswon’tinfectyourcomputerwithavirus.Theviruscodehastobeinaform,suchasan.exeprogr