Computer Malware
Malware Definition
Malware, short for malicious software, is any software used to disrupt
computer operations, gather sensitive information, gain access to private
computer systems, or display unwanted advertising.
Malware is defined by its malicious intent, acting against the requirements
of the computer user, and does not include software that causes
unintentional harm due to some deficiency.
The term badware is sometimes used, and applied to both true (malicious)
malware and unintentionally harmful software.
Malware is an abbreviated term meaning “malicious software.” This is
software that is specifically designed to gain access or damage a
computer without the knowledge of the owner.
Common Types of Computer Malware
Viruses
Worms
Bombs- Logic and Time
Trojan Horse
COMPUTER VIRUSES
A computer virus is a program that has the ability to reproduce/replicate
itself without the user’s knowledge.
For example, it may attach itself to the DOS program FORMAT and run
every time you format a diskette.
There are other types of software that can cause problems in a PC.
However, no other software can replicate and it is this characteristic that
makes a program a virus.
Effects of Viruses:
A virus can destroy/delete or corrupt data e.g. those on specific
applications such as all Excel files or all word files e.g. Sircam worm
deletes data.
Display irritating message, or otherwise disrupt computer operations.
Most viruses stay in your PC’s memory where they can cause problems by
interfering with other software you are trying to run.
Disable hardware, making the computer unusable.
It can perform dangerous operations like formatting the hard disk.
It consumes the disk space, memory and wastes the processor time.
Once you have a virus, it is very likely that you will pass it on to a
colleague or a customer, who may well lose confidence in you and your
company.
Types of Viruses:
File viruses:
A file virus infects the executable program files on your computer
system.
These usually, but not always, have COM or EXE file extensions. When you
run an infected program, your computer also runs the attached virus
instructions to replicate or to deliver its payload.
The term payload refers to the ultimate mission of a virus. For example,
the payload of the “stoned” virus is the message,” your Pc is now stoned”.
Only a few viruses such as Cinderella and Frodo, are designed to infect
data files.
Because a virus needs to be executed to spread, a data file can only be a
carrier, it cannot deliver the payload.
Boot Sector Viruses
These infect the system files your computer uses every time you turn it
on. The boot sector is the part of every hard disk and diskette, which is
read by the computer every time you start it up.
The partition sector, also called the Master Boot Record (MBR), is the first
part of the hard disk to be read after the system has started up.
It contains information such as the number of sectors in each partition and
the location of all the partitions.
If your booting disk is infected and you try to boot your computer with it
then the following message is likely to be displayed.
Non-system disk or disk error
Replace and press any key when ready.
By this time the virus has already run and your PC may already be
infected. In most cases, the virus loads itself into memory and infects the
partition sector of the hard disk.
It replaces the original partition sector with its own code. If this partition
sector is infected, when the PC is rebooted from the hard disk, the virus is
loaded into memory. Any diskette subsequently accessed is infected.
Companion Viruses
If you have a COM file and an EXE file of the same name, Dos always runs
the COM file in preference to the EXE file is not file extension is given.
Companion viruses make use of this fact by creating COM files with the
same name as the legitimate EXE files, thus ensuring they are executed.
They then pass control to the original EXE file which runs normally.
Symptoms of the Viruses
The symptoms of a virus infection depend on the virus. The following
symptoms might indicate that your computer has contracted a virus.
However, some of these symptoms can have other causes.
Your computer displays annoying messages such as “Gotcha! Arf Arf!
“You are stoned”
Your computer develops unusual visual or sound effects. For example,
characters begin to disappear from your screen or the sound of a flushing
toilet comes for your computer’s speakers.
You have difficulty saving files.
Your computer suddenly seems to work very slowly.
Files are mysteriously missing.
Your computer reboots unexpectedly.
Your executable files unaccountably increases in size.
Viruses are just one type of program in a large category of software
designed by hackers to disrupt or damage the data on computers.
Other Potential Problems are:
Trojan Horse
A Trojan horse is a computer program that appears to perform one
function while actually doing something else. They are less widespread
than viruses because they do not replicate, but they can represent a
threat when copied. A Trojan horse sometimes, but not always, harbors a
virus.
For example, a hacker may write a program to format hard disk drives and
embeds this program in a file called sched.exe. He then distributes the
disk containing this Trojan and posts it to computer bulletin boards where
other users are likely to assume that it is a free scheduling program, just
to realize that it has deleted all the files upon execution. This Trojan
horse does not harbor a virus because it does not replicate itself.
Another popular Trojan horse looks like the login screen on a network.
However, as a user logs in, the Trojan horse collects the user’s ID and
password. These are stored in a file that hackers can access later.
Armed with a valid user ID and password, the hackers can access the data
stored on the network.
Time Bombs and Logic Bombs
A time bomb is a computer program that stays in your system
undetected until it is triggered by a certain event in time, such as when a
computer system clock reaches a certain date. It is usually carried by a
Trojan horse or a virus.
A notorious time bomb appeared in December 1989. Many hospitals and
medical clinics received in innocent looking package containing “ADS
information” software from a company called PC Cyborg. The process of
installing the software also installed a time bomb. After the computer
was booted a certain number of times, the time bomb scrambled the data
on the hard disk. Next, the bomb displayed an invoice demanding
payment before the method for unscrambling the hard disk was revealed.
A logic bomb is a computer program that is triggered by a specific set of
conditions, such as the number of files in a disk, or a certain sequence of
characters being entered. It can be carried by a virus or a Trojan horse.
But it could also be a stand alone program.
Worms
A software worm is a program designed to enter a computer system –
usually a network through security holes.
Like a virus, a worm reproduces itself. Unlike a virus, a worm does not
need to be attached to an executable program to reproduce.
These security holes may be electronic mail system.
How Worms Spread
Through data transfer; either through auxiliary storage devices, or from
one computer to the other through networking.
It is spread when an infected program is executed or the computer is
booted from infected diskette.
Through electronic communication devices/times as attached to emails.
Control/Avoidance and Detection
Avoid using high-risk disks programs e.g. disks containing public domain
software or shareware and on disks containing illegal copies of computer
programs downloaded form bulletin boards. You must use a virus
detection program to check for viruses before you run any programs from
such disks.
Use of virus detection program/ updated anti-virus programs which
examines the files stored on a disk to determine if they are infected with a
virus, then disinfects the disk, if necessary.
Backups – make regular backups of your system.
Write-protect all boot diskettes. Viruses cannot infect manually protected
diskette.
CONSUMER’S GUIDE TO DESKTOP COMPUTER SYSTEMS
When buying a new computer you must look at the specifications
describing the computer’s components, capabilities, and special features.
The following specifications will help you:
Comparing Microprocessors
The Cost and benefits of RAM cache.
RAM requirements
The number and type of floppy disk drive needed
Hard Drive Specifications.
The system unit case.
Video Adapters and Monitors
Sound card
Selecting a modem
Many computer systems include internal modems that transmit to and
receive data from other
The value of bundled Software
