COM111 Lecture Schedule 10

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:

            1. www.google.com

            2. www.altavista.com

            3. www.lycos.com

            4. www.hotbot.com

                        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

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

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

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.