翻译.docx

翻译.docx

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翻译

VirusesofComputer

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.Newvirusescomeouteverysingleday;ana-vprogramthathasn’tbeenupdatedforseveralmonthswillnotprovidemuchprotectionagainstcurrentviruses.

Inadditiontoscanningforvirusesonaregularbasis,installan‘onaccess’scanner（includedinmostgooda-vsoftwarepackages）andconfigureittostartautomaticallyeachtimeyoubootyoursystem.Thiswillprotectyoursystembycheckingforviruseseachtimeyourcomputeraccessesanexecutablefile.

Fileinfectorscanbeeitherdirectactionorresident.Adirect-actionvirusselectsoneormoreotherprogramstoinfecteachothertimetheprogramwhichcontainsitisexecuted,andthereafterinfectsotherprogramswhen“they”areexecuted（asinthecaseoftheJerusalem）orwhencertainotherconditionsarefulfilled.TheViennaisanexampleofadirect-actionvirus.Mostothervirusesareresident.Newvirusescomeouteverysingleday;ana-vprogramthathasn’tbeenupdatedforseveralmonthswillnotprovidemuchprotectionagainstcurrentviruses.

Inadditiontoscanningforvirusesonaregularbasis,installan‘onaccess’scanner（includedinmostgooda-vsoftwarepackages）andconfigureittostartautomaticallyeachtimeyoubootyoursystem.Thiswillprotectyoursystembycheckingforviruseseachtimeyourcomputeraccessesanexecutablefile.

Thesecondclassissystemorboot-recordinfectors:

thoseviruses,whichinfectexecutablecode,foundincertainsystemareasonadiskthatarenotordinaryfiles.OnDOSsystems,thereareordinaryboot-sectorviruses,whichinfectonlytheDOSbootsectorondiskettes.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:

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