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Computing |
Internet Security If you have read the last article, I assume that you have become familiar with the definition and anatomy of a computer virus. As in medicine, in cases of Computer viruses too we have specialization depending on area of infection and amount of damage. So let us study the basic category of viruses. Types of viruses Boot viruses: These
viruses infect floppy disk boot records or master boot records in hard
disks. They replace the boot record program (which is responsible for
loading the operating system in memory) copying it elsewhere on the disk
or overwriting it. Boot viruses load into memory if the computer tries
to read the disk while it is booting. Program viruses:
These infect executable program files, such as those with extensions
like .BIN, .COM, .EXE, .OVL, .DRV (driver) and .SYS (device driver).
These programs are loaded in memory during execution, taking the virus
with them. The virus becomes active in memory, making copies of itself
and infecting files on disk. Multipartite viruses:
A hybrid of Boot and Program viruses. They infect program files and when
the infected program is executed, these viruses infect the boot record.
When you boot the computer next time the virus from the boot record
loads in memory and then starts infecting other program files on disk. Stealth viruses:
These viruses use certain techniques to avoid detection. They may either
redirect the disk head to read another sector instead of the one in
which they reside or they may alter the reading of the infected file’s
size shown in the directory listing. For instance, the Whale virus adds
9216 bytes to an infected file; then the virus subtracts the same number
of bytes (9216) from the size given in the directory. Polymorphic viruses:
A virus that can encrypt its code in different ways so that it appears
differently in each infection. These viruses are more difficult to
detect. Macro Viruses: A
macro virus is a new type of computer virus that infects the macros
within a document or template. When you open a word processing or
spreadsheet document, the macro virus is activated and it infects the
Normal template (Normal.dot)-a general purpose file that stores default
document formatting settings. Every document you open refers to the
Normal template, and hence gets infected with the macro virus. Since
this virus attaches itself to documents, the infection can spread if
such documents are opened on other computers. Active X: ActiveX and Java controls will soon be the scourge of computing. Most people do not know how to control there web browser to enable or disable the various functions like playing sound or video and so, by default, leave a nice big hole in the security by allowing applets free run into there machine. There has been a lot of commotion behind this and with the amount of power that JAVA imparts, things from the security angle seem a bit gloom. These are just few broad categories. There are many more specialized types. But let us not go into that. We are here to learn to protect our self, not write a thesis on computer virus specification.
– Mayur Kamat
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