There are 10 main types of viruses that are classified based on their behavior and abilities: boot sector viruses, companion viruses, encrypted viruses, logic bomb viruses, macro viruses, multipartite viruses, nonresident viruses, polymorphic viruses, resident viruses, and stealth viruses. Each type has distinct characteristics, such as boot sector viruses' ability to hide in the boot sector and load at system boot, companion viruses' creation of additional files in the same directory, and stealth viruses' capability to intercept antivirus requests to hide from detection. In summary, viruses are classified into these 10 main types depending on their infection mechanisms and goals.

1. 10 types of virus
There are manytypesof viruses,some cause harmlessbutsome cause devastating.Theyare classified
intodifferencecategoriesincludingBootSectorViruses,CompanionViruses,EncryptedViruses,Logic
BombViruses,Macro Viruses, Multipartite Viruses,NonresidentViruses,PolymorphicViruses,Resident
VirusesandStealthViruses.Youcansee the explanationof eachtype of virusesinfollowing:
1. Boot SectorViruses
Thistype of viruseshasabilitytohide inbootsector.The viruseswill loadintomemorywhenthere is
bootingsystem andtryingtoread fromhard disk.Bootsector virusesare more spreadsince oldtime
whenfloppydiskwaspopular.Butnowwe hardlyseenthemsince manyof themonlycanspread
throughfloppydisk.
2. CompanionViruses
CompanionVirusesisanotherkindof viruses.Whenusercomputerinfectbythissortof viruses,itwill
create anothertype file fromanexistingfile insame directory(suchas creatingfile.comfromfile.exe in
the same folder),some companionvirusescreate file.exefromanyfolder.
3. EncryptedViruses
Thistype of virusesconsistsof encryptedmaliciouscode,decryptedmodule.The virusesuse encrypted
code technique whichmake antivirussoftwarehardlytodetectthem.The antivirusprogramusuallycan
detectthistype of viruseswhentheytryspreadbydecryptedthemselves.
4. Logic Bomb Viruses
Logic BombVirusesorsometime knowasTime Bombissmall piece of maliciouscode orprogramwhich
have abilitytoinsertitself tootherprogramsorsystemandperformspecific actionwhenthe conditions
are met(mostLogic Bombdevelopersuse date asconditions).The LogicBombdoesnothinguntil pre-
programmeddate isreached.LogicBomb can performanymaliciousthingsbasedonpre-programmed
withinitsuchas deletingfile ordisplayingunwantedmessage orlockprogramand so on.
5. Macro Viruses
WhentalkingaboutMacro Viruses,we refertoviruseswhichinfectmacroof otherapplicationssuchas
MicrosoftWord, MicrosoftExcel.The virusesare writteninamacro language and use itto distribute
themselves.Macroviruseswill runautomaticallywhenuseropendocument.Usuallythistype of virus
cause harmlesstoyour computer,butinsteadtheyare annoyingbyautomaticallyinsertingundesired
textsor symbols.
Example of Macro Virus:WM.Concept,itwas introducedin1995 the firstmacro virusthat spread
throughMicrosoftWord. Andanotherpopularone isMelissathatis firstfoundin1999, italsocan
spreadthrough MS Word,Excel and Outlook.

2. 6. Multipartite Viruses
Multipartite Virusesistype of viruseswhichinfectusercomputeronbothpartboot sectorand
executable filesandprogramsat the same time,withthiscondition,the virusesspreadfasterthanboot
sectoror file infectoralone.
Example:Ghostball,the firstmultipartite virus.
7. NonresidentViruses
Thistype of virusesissimilartoResidentVirusesbyusingreplicationof module.Besidesthat,
NonresidentVirusesrole asfindermodule whichcaninfecttofiles whenitfoundone (itwill selectone
or more filestoinfecteachtime the module isexecuted).
8. PolymorphicViruses
PolymorphicVirusissimilartoencryptedviruses;itcaninfectfileswithanencryptedcopyof itself.The
virusesuse difference technique toreplicate themselves.Some polymorphicvirusesare hardlytodetect
by antivirussoftware usingvirussignaturebased,becauseitdonotremainany identical after
replication.
Example:Pseudonym,1260
9. ResidentViruses
ResidentVirusesorknownasMemoryResidentVirusesismaliciousmodule.The virusescanreplicate
module and installingmaliciouscode intocomputermemory(RAM).The virusesare commonlyclassified
intotwo maincategories:FastInfectorsandSlow Infectors.
10. StealthViruses
StealthVirusesissome sortof viruseswhichtrytotrick anti-virussoftwarebyinterceptingitsrequests
to the operatingsystem.Ithasabilitytohide itself fromsome antivirussoftware programs.Therefore,
some antivirusprogramcannotdetect them.
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