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ID:22430899
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页数:9页
时间:2018-10-29
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1、职场大变样社区(www.zcdby.com):下载毕业设计成品全套资料,全部50元以下英文文献及中文翻译VirusIntroductionViruseswillcausemuchconfusion.Evensomevirus“experts”willmisinformthecauseofthevirus.Let’sdefinewhatwemeanbyvirus.Avirusisaprogramthatreproducesitsowncodebyattachingitselftootherexecutablefiles,sotheviruscodeisexecutedwhentheinf
2、ectedexecutablefileisexecuted.Here,theprogram(COMorEXEfile)referstoanexecutablefile.Toattachmightmeanphysicallyaddingtotheendofafile,insertingintothemiddleofafile,orsimplyplacingapointertoadifferentlocationonthedisksomewherewheretheviruscanfindit.Mostvirusesplaceself-replicatingcodesinotherprogr
3、ams,sothatwhenthoseotherprogramsareexecuted,evenmoreprogramsare"infected”withtheself-replicatingcodes.Theseself-replicatingcodes,whencausedbysomeevent,maydoapotentiallyharmfulacttoyourcomputer.Themacroportionofadatafilemaybemuchmorecritical(e.g.,aMicrosoftWorddocument),butlessobvious.Morerecentl
4、y,scriptswrittenforInternetwebsitesand/orincludedinE-mailcanalsobeexecutedandinfected.Similartoviruses,youcanalsofindmaliciouscodesinTrojanHorses,worms,andlogicbombs.VirusBehavior—InfectionPhaseViruseshavemanydifferentforms,buttheyallpotentiallyhavetwophasestotheirexecution:theinfectionphaseandt
5、heattackphase.Nowwefirstlydiscusstheinfectionphase.Whenthevirusexecutesitcaninfectotherprograms.Somevirusesinfectotherprogramseachtimetheyareexecuted;othervirusesinfectonlyuponacertaincause.Thiscausecouldbeanything,adayortime,anexternaleventonyourPC,acounterwithinthevirus,etc.Viruswriterswantthe
6、irprogramstospreadasfaraspossiblebeforeanyonenoticesthem.ManyvirusesgoresidentinthememoryofyourPC(likeTSR).Thevirusmaysilentlyresidentinmemorywaitingforyoutoaccessadiskette,copyafile,orexecuteaprogram,beforeitinfectsanything.Becausethecauseconditiontheyusefortheirinfectionishardtoguess,virusesar
7、emoredifficulttoanalyze.ResidentvirusesfrequentlytakeoverportionsofthesystemsoftwareonthePCtohidetheirexistence.Thistechniqueiscalledstealth.Polymorphictechniquesalsohelpvirusestoinfectyetavoiddetection.Notethatwormsoftentak
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