COM111 Lecture
Schedule 10
Search
Engines, Instant Messaging, Computer Security, Current Trends in Computer
Networks and Internet.
•
The amount of information on the Web is
vast. Since there is no possible way to know every address of every Web site to
be visited.
•
Hence to conduct search on the Internet,
a special search tool known as search
engines are used.
•
A search engine is a searchable database
of Internet files collected by a computer program called a Wander, Crawler, Robot, Worm or Spider.
•
A search engine is an application on the
web that allows you to search for particular web sites based on key words or
concepts .
•
A search engine
consists of three components:
1. Spider: Program that traverses the Web from link to
link, identifying and reading
pages.
2. Index: Database containing a copy of each Web page
gathered by the spider.
3. Search Engine Mechanism: Software
that enables users to query the index and
usually returns results in term relevancy ranked order.
Searching the Internet:
Some of the well
known search engines are:
First
open the search engine’s web site (Ex. www.google.com) . Now type your
keyword(s) in the search box and click the button search or go.
Refining the Search:
The major search engine allow the user to
choose whether to search for the exact typed phrase, all the words in the
phrase, any of the words in a phrase, and so on. But fee search engines do not
provide such option. In this case, the user can define the search by adding one
or more words or symbols to the search topic.
•
AND: used to search for
two or more terms on the same page. Type the word AND between the terms ( ex.
fruits AND crops) or put a plus sign
right before the second term ( ex. fruits + crops)
•
OR : Used to search for either of two or more terms
on the same page. Type the word OR between the terms (ex. College OR University)
•
NOT: used to search for pages that include the
first term but not the second. Type the word NOT between the terms ( ex.
cats NOT dogs) or put a minus sign right
before the second term ( ex. fruits - mango)
•
“ ”: Double quotes are
used to search for an exact phrase.
Ex.1 “Tissue culture” Ex 2: “desktop wallpapers”
•
( )
: Parenthesis are used to group parts of the search phrase.
Ex. Type desktop AND (themes OR
wallpapers) . This returns pages with
the
words
desktop and themes or both the words themes and wallpapers.
•
*
:Asterisk is used to search for
various forms of a word.
Ex:
prior* returns pages with the words
prior, priorities, priority and so on.
Instant Messaging
·
Instant messaging is a web-based service
to exchange messages in real time between two or more people over the Internet.
·
It is a combination of e-mail and chart
room. Users create a list of users with whom they wish to communicate.
·
To send and receive instant messages,
Internet connection along with instant messaging software (Example Yahoo
Messenger, MSN Messenger ) are required.
·
It is free and faster than e-mail because
instant messages can be sent to friends whether they are online or offline.
·
Users send their messages in text format.
·
A user can also communicate through web
cam (Video chatting) as well as through speakers and microphone (Voice
chatting).
·
One can send audio or video files along
with instant messages.
Features of Messenger
·
Chatting : One can chat using
a web cam or microphone and send textual messages.
·
Audibles: Used for sending
verbal animations (greetings, games and fun) directly.
·
Emoticons / Smileys: Used to express the
feelings in the form of little symbols and
smiling faces.
·
Games : When connected
online, users can play multi-player games such as chess,
checkers etc.
·
Address book : Messengers also
provide address books so that users can easily find and manage their friend’s
contact details.
Computer Security
·
Computer security refers to the
protection given to computers and the information contained in them from
unauthorised access.
·
A technological and managerial procedure applied to secure the
computer system.
·
Computer security and its policies,
procedures and tools that are necessary to protect the computer system.
·
It involves the measures and controls
that ensure confidentiality, integrity
and availability.
·
These three aspects are responsible for
effective computer security.
Confidentiality:
· It ensures that
information is available only to those persons who are authorised to access it.
· The most common form
of access control is the use of Passwords. Therefore, keeping password
confidential is one of the most fundamental principles of computer security.
Integrity:
·
It ensures that information cannot be
modified in unexpected ways. For this, encryption process is used, which
transforms information into some secret form to prevent unauthorised
individuals from accessing the data.
Availability:
·
It prevents resources from being deleted
or becoming inaccessible.
· It ensures that
needed resources are usable when and where needed, thus providing system
redundancy, in the form of backup data and power source.
Security Threats
· Computer systems are
vulnerable to many kinds of threats that can cause various types of damages,
which may result in significant data loss.
· A threat can come
from any person, object, or event that, if realised could potentially cause
damage to the computer network.
Some
of the commonly occurring threats to a network are
1.
Errors and omissions
Errors and omissions
are important threats to data and system integrity. These errors are caused not
only by data entry operators, processing hundreds of transactions per day, but
also by users who create and edit data.
2.
Loss of physical and
infrastructure support
The infrastructure
support includes power failures, loss of communications, water outages and
leaks. More loss is associated with fires and floods than with viruses.
3.
Hacker and Cracker
The term hacker refers to
the person, who breaks into computers without authorisation. The threat
generated from a hacker should be
considered in terms of the past and potential future damage.
Another class of people
called cracker also poses security threat. Cracker is an individual who
attempts to access computer systems without authorisation. These individuals as
opposed to hackers destroy the data once into another computer system.
4.
Malicious code and
software
Malicious codes are the software
programs that generate threats to the computer system and precious data. This
code can be in the form of viruses, worms, Trojan horses, Logic bombs and other
uninvited software
5.
Foreign government
espionage
Threats can be posed
by foreign government intelligence services. by foreign government intelligence
services may target unclassified systems to collect intelligence missions.
Unclassified information includes travel plans of senior officials, defence,
satellite data, personnel data, security files etc.
MALICIOUS PROGRAMS:
The malicious
programs are often called Virus, Worms, Trojan horse, logic bomb, spyware and
so on
VIRUS
•
A program or piece of code that is loaded
onto your computer without your knowledge and runs against your wishes.
•
Viruses can also replicate themselves.
All computer viruses are manmade.
•
A simple virus that can make a copy of
itself over and over again is relatively easy to produce.
•
Even such a simple virus is dangerous
because it will quickly use all available memory and bring the system to a
halt.
•
An even more dangerous type of virus is
one capable of transmitting itself across networks and bypassing security
systems.
•
A computer virus is a computer program
that can copy itself and infect a computer. The term "virus" is also
commonly but erroneously used to refer to other types of malware, adware, and
spyware programs that do not have the reproductive ability. A true virus can
only spread from one computer to another (in some form of executable code) when
its host is taken to the target computer.
•
The major difference between a computer
virus and spyware is that spyware does not replicate itself. A computer virus
will gain entry onto your computer using only one file and replicate its code
many times onto other files in your computer. Spyware is generally contained to
one file and can easily be deleted to rid your system of the problem.
What viruses don't do
Ø Computer viruses
cannot infect write protected disks or infect written documents.
Ø Viruses do not infect compressed files, unless
the file was infected prior to the compression. [Compressed files are programs
or files with its common characters, etc. removed to take up less space on a
disk.]
Ø Viruses do not infect computer hardware, such
as monitors or computer chips; they only infect software.
Ø In addition, Macintosh viruses do not infect
DOS / Window computer software and vice versa. For example, the Melissa virus
incident of late 1998 and the ILOVEYOU virus of 2000 worked only on Window
based machines and could not operate on Macintosh computers
WHAT VIRUSES CAN DO
Ø An annoying message
appearing on the computer screen.
Ø Reduced memory or
disk space.
Ø Modification of
data.
Ø Files overwritten or
damaged.
Ø Hard drive erased.
Types of computer viruses
1. Macro Viruses: Macro Viruses are
one of the most commonly seen computer viruses. These are platform independent
viruses and hence they are seen in applications. They will be making the
application malfunctioning and thus we won’t be getting the desired results out
of it. These viruses are ported directly into the desired applications for
which it has been written. But don’t think that they won’t be doing any harm to
other parts of your system. They will surely be harming the whole performance
of your computer.
Examples: DMV, Nuclear, Word Concept.
2. 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.
Examples: Form, Disk Killer, Michelangelo, and Stone virus
Examples: Form, Disk Killer, Michelangelo, and Stone virus
3. 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.
Examples: Involuntary, Stimulate, Cascade, Phoenix, Evil, Proud, Virus 101
Examples: Involuntary, Stimulate, Cascade, Phoenix, Evil, Proud, Virus 101
4. Trojan Horse: Strictly speaking, a
Trojan horse is NOT a virus
because it does not replicate like ordinary viruses do. A Trojan horse is an
unfriendly program which will appear to be something other than what it is, for
example a program that is disguised as a legitimate software program. The
Trojan virus once on your computer, doesn't reproduce,. Making this type of
virus extremely dangerous to your computer's security and your personal
privacy. Therefore, you should avoid downloading programs or files from sites
if you're not 100 percent positive of what the file or program does. Below are
some common Trojans:
Back Orifice 2000 : BO2K allows outsiders to access and
modify any information on a Windows 95, 98 and NT machines through an invisible
server program installed by the program. It also allows outsiders to spy on
what user is doing. BO2K is expected to be released on 10/7/1999.
5. 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.
Examples: Sunday, Cascade
Examples: Sunday, Cascade
6. 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. A stealth
virus actively hides the changes it has made to the hard disk so that it appears
that it has not infected the system.
Examples: Frodo, Joshi, Whale
7. WORM:
A Worm is a virus program
that copies and multiplies itself by using computer networks and security
flaws. Worms are more complex than Trojan viruses, and usually attack multi-user
systems such as Unix environments and can spread over corporate networks via
the circulation of emails. Once multiplied, the copied worms scan the network
for further loopholes and flaws in the network. A classic example of a worm is
the ILOVEYOU virus.
The best way you can protect
yourself from worms is by updating your security patches. Operating systems and
application vendors normally provide these patches. In addition, you should
avoid opening email attachments from unknown senders.
A worm is similar to a virus by its design, and is considered to be
a sub-class of a virus. Worms spread from computer to computer, but unlike a
virus, it has the capability to travel without any help from a person
Virus Preventive
& Corrective Measure / Protecting Computer System
Antivirus
•
Antivirus (or anti-virus) software is used to
prevent, detect, and remove malware, including computer viruses, worms, and
Trojan horses.. Such programs may also prevent and remove adware, spyware and
other forms of malware(malicious software)
•
A software utility that searches a hard
disk for viruses and removes any that are found. Most antivirus programs
include an auto-update feature that enables the program to download profiles of
new viruses so that it can check for the new viruses as soon as they are
discovered.
•
These programs scan the code of every
file on your computer for traces of viruses and spyware, and if found, the file
is quarantined until the code can be removed or the file deleted.
Functions of Anti-viruses.
Ø Protection
Antivirus software can
provide real-time protection, meaning it can prevent unwanted processes from
accessing your computer while you surf the Internet.
Ø Cleanup
Antivirus software allows
you to scan your computer for viruses and other unwanted programs, and provides
you with the tools to get rid of them.
Ø Alerts
Antivirus programs can alert
you when something is trying to access your computer, or when something in your
computer is trying to access something on the Internet.
Ø Updates
Antivirus programs can
update themselves, keeping your computer's protection up to date without you
having to manually update it.
Ø Further Protection
If an antivirus software
finds an infected file that cannot be deleted, it can quarantine the file so
that it cannot infect other files or programs on your computer.
Firewall:
It
is an application, which prevents outside connections from entering into the
network. It traps inbound or outbound packets, analyses them, and then permits
access or discards them. It is typically implemented using one of three primary
architectures
·
Packet filtering
It is basic firewall protection technique,
which operates at the network layer to examine incoming and outgoing packets
·
Circuit-level gateway
Monitors connections that are found
to be valid. It allows relevant packet to pass through the firewall
·
Application – level gateway
Uses server programs that run on the
firewall. These proxies take external requests, examine them, and forward
requests to the internal host.
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