高中英语：virus相关素材（牛津版选修7）.doc

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Virus
Incomputers,avirusisaprogramorprogrammingcodethatreplicatesbybeingcopiedorinitiatingitscopyingtoanotherprogram,computerbootsectorordocument.Virusescanbetransmittedasattachmentstoane-mailnoteorinadownloadedfile,orbepresentonadisketteorCD.Theimmediatesourceofthee-mailnote,downloadedfile,ordisketteyou'vereceivedisusuallyunawarethatitcontainsavirus.Someviruseswreaktheireffectassoonastheircodeisexecuted;othervirusesliedormantuntilcircumstancescausetheircodetobeexecutedbythecomputer.Somevirusesarebenignorplayfulinintentandeffect("HappyBirthday,Ludwig!")andsomecanbequiteharmful,erasingdataorcausingyourharddisktorequirereformatting.Avirusthatreplicatesitselfbyresendingitselfasane-mailattachmentoraspartofanetworkmessageisknownasaworm.
Generally,therearethreemainclassesofviruses:
Fileinfectors.Somefileinfectorvirusesattachthemselvestoprogramfiles,usuallyselected.COMor.EXEfiles.Somecaninfectanyprogramforwhichexecutionisrequested,including.SYS,.OVL,.PRG,and.MNUfiles.Whentheprogramisloaded,thevirusisloadedaswell.Otherfileinfectorvirusesarriveaswholly-containedprogramsorscriptssentasanattachmenttoane-mailnote.
Systemorboot-recordinfectors.Thesevirusesinfectexecutablecodefoundincertainsystemareasonadisk.TheyattachtotheDOSbootsectorondiskettesortheMasterBootRecordonharddisks.Atypicalscenario(familiartotheauthor)istoreceiveadiskettefromaninnocentsourcethatcontainsabootdiskvirus.Whenyouroperatingsystemisrunning,filesonthediskettecanbereadwithouttriggeringthebootdiskvirus.However,ifyouleavethedisketteinthedrive,andthenturnthecomputerofforreloadtheoperatingsystem,thecomputerwilllookfirstinyourAdrive,findthediskettewithitsbootdiskvirus,loadit,andmakeittemporarilyimpossibletouseyourharddisk.(Allowseveraldaysforrecovery.)Thisiswhyyoushouldmakesureyouhaveabootablefloppy.
Macroviruses.Theseareamongthemostcommonviruses,andtheytendtodotheleastdamage.MacrovirusesinfectyourMicrosoftWordapplicationandtypicallyinser