Some viruses are named in a particular way depending on who possess less certain characteristics:
polymorphic virus a virus, usually plaintext is encrypted, leaving only the decryption routine. A polymorphic virus changes the code of the decryption routine for each new infection (obviously leaving unchanged the algorithm) by means of inserting junk code, permutation code, etc ...
metamorphic virus-like polymorphic virus, however, is capable of completely changing their code, is more powerful than polymorphic viruses as some anti-virus software can recognize a virus from the code during execution. Also sometimes employ advanced masking techniques based on the division of your code and then push the parties in different parts of the infected file (virus Conventional enter the code in full in the bottom of the file, changing the entry point to the malicious code to execute first), also leaving unchanged the entry point to make it even more difficult for the virus. It must be said also that the encryption of metamorphic virus is not required. Exe virus
viruses that infect executable files. EXE.
com virus virus that infects files command. COM (now rare).
companion virus
viruses that exploit the characteristics of the MS-DOS is to run a command file first. And then a COM executable. EXE in the case have the same file name (eg between Program.exe and PROGRAM . COM if you start without specifying PROGRAM l'estensione verrà prima lanciato PROGRAM.COM), in questo modo i virus creano dei "gemelli" (companion) che sono copie del virus stesso che, dopo essere stati eseguiti, lanciano il relativo .EXE mascherandosi (ormai rari).
virus di boot
un tipo di virus ormai poco diffuso, che infetta il boot sector dei dischi (floppy disk o hard disk) invece che i singoli file.
macrovirus
può essere contenuto generalmente in un documento di Microsoft Word, Microsoft Excel o Microsoft PowerPoint e consiste in una macro; può diffondersi a tutti i documenti che vengono aperti con quella particolare applicazione. Questo tipo di virus può infettare i sistemi operativi su cui gira ms-office (windows e mac), anche se non è detto che possano funzionare correttamente su altri sistemi operativi coinvolti.
retrovirus
virus che si annida nei programmi antivirus e li mette fuori uso. Il nome deriva dai retrovirus biologici, in grado di attaccare il sistema immunitario (come, ad esempio, l'HIV).
virus multipiattaforma
ci sono stati vari tentativi per creare virus che infettassero più sistemi operativi funzionanti sotto la stessa architettura hardware e lo stesso processore, ma si sono rilevati degli insuccessi o hanno avuto un successo molto limitato. Un esempio è il virus winux [1] che in teoria può infettare sia i sistemi operativi della Microsoft che quelli unix-like (es: GNU/Linux) giranti sotto CPU x86. In general, these types of multi-platform virus can be difficult to put on a Unix-like: the spread usually occurs only if the user performs a mail attachment, which is already perceived as quite remote, and because an attachment, you just saved can not be executed unless the execute permissions are assigned, then you can discard the extent that performance is accidental, in other cases even be the root user to run the attachment, even more impossible for those who knows how to operate a system of this type. The success of this type of virus is confined to the front of the operating systems of Microsoft, where instead you can almost always run an attachment, even by mistake.
