Computer Introduction-Lecture04 for applied scince college students, Seiyun University , yemen 2023-2024 Academic year. لطلاب كلية العلوم التطبيقية بجامعة سيئون مقدمة في علوم الحاسوب المحاضرة الرابعة

1. Lecture No. 4: Computer Viruses
Lecturer: Dr. Mazin Alkathiri
Department of Computer Science,
Faculty of Applied Science,
Seiyun University
2023

2. Computer Viruses
A virus is a computer code or malware program, which is
capable of affecting computer data badly by corrupting or
destroying them. cause a computer to behave in unexpected
ways, or interfere with the operation of the network, all while
concealing and replicating itself.
The defining characteristic of viruses is that they are self-
replicating computer programs which install themselves without
the user's consent.

3. ◦ Some virus writers consider their creations to be works of art, and see virus
writing as a creative hobby.
◦ Viruses have been written as research projects, pranks, vandalism, to attack the
products of specific companies.
◦ Some viruses were intended as "good viruses". They spread improvements to the
programs they infect, or delete other viruses.
 These viruses are, however, quite rare, still consume system resources, may accidentally
damage systems they infect.

4.  Following are the major types of computer virus −
1. Worms
This is a computer program that replicates itself at a swift pace. Unlike a computer
virus, it is self-contained and hence does not need to be part of another program to
propagate itself.
• burrow through and between networks to change or overwrite data.

5. 2. Trojan Horse
A Trojan Horse is also a sort of destructive program that remains disguised in a normal
software program.
 appear to be legitimate programs but when opened, damage software codes.

6. 3. Bombs
It is similar to Trojan Horse, but Logic bombs have some specialty; these include a
timing device and hence it will go off only at a particular date and time.

7.  Boot Sector Virus
◦ Infects the boot or MBR of diskettes and hard drives
through the sharing of infected disks and pirated software
applications
◦ Once your hard drive is infected all diskettes that you use in
your computer will be infected
 Program Virus
◦ Becomes active when the program file (usually with
extensions .BIN, .COM, .EXE, .OVL, .DRV) carrying the virus
is opened
◦ It then makes copies of itself and will infect other programs
on the computer
 Multipartite Virus
◦ Hybrid of a Boot Sector and Program viruses
◦ It infects program files and when the infected program is
active it will affect the boot record

8.  Stealth Virus
◦ Disguises itself to prevent from being detected by antivirus
software
◦ It alters its file size or conceals itself in memory
 Polymorphic Virus
◦ Act like a chameleon, changing its virus signature (binary
pattern) every time it multiples and infects a new file
 Macro Virus
◦ Programmed as a macro embedded in a document, usually
found in Microsoft Word and Excel
◦ Once it gets in to your computer, every document you
produce will become infected
◦ Relatively new type of virus and may slip by your antivirus
software if you don't have the most recent version installed

9. 1. Mydoom – $38 billion – 2004
Also known as Novarg, this malware is technically a “worm,” spread by mass emailing
2. Sobig – $30 billion - 2003
This cybercriminal program masqueraded as legitimate computer software attached to emails.
3. Klez – $19.8 billion – 2001
The Klez worm sent fake emails, spoofed recognized senders and, among other things, attempted to deactivate other
viruses.
4. ILOVEYOU – $15 billion – 2000
Worked by sending a bogus “love letter” that looked like a harmless text file.
5. WannaCry – $4 billion - 2017
Ransomware, a virus that takes over your computer (or cloud files) and holds them hostage.
6. Zeus – $3 billion – 2007
Online theft tool that hit the web
7. Code Red – $2.4 billion – 2001
Another worm that penetrated 975,000 hosts.
8. Slammer – $1.2 billion – 2003
It used these victim machines to launch a DDoS attack on several internet hosts, significantly slowing internet traffic.
9. CryptoLocker – $665 million – 2013
Ransomware attacks - This malware attacked upwards of 250,000 machines by encrypting their files.
10. Sasser – $500 million - 2004
worm was written by a 17-year-old German computer science student named Sven Jaschan.
 Computer viruses cost an estimated $55 billion each year in cleanup and repair costs. The biggest
computer virus ever is the Mydoom virus, which did an estimated $38 billion in damages in 2004.

10.  By downloading files from the Internet.
 During the removable of media or drives.
 Through pen drive.
 Through e-mail attachments.
 Through unpatched software & services.
 Through unprotected or poor administrator passwords.

11.  impact of virus on computer systems −
 Disrupts the normal functionality of respective computer system.
 Disrupts system network use.
 Modifies configuration setting of the system.
 Destructs data.
 Disrupts computer network resources.
 Access confidential data.

12.  The most fundamental method of detection of virus is to check the functionality of
your computer system; a virus affected computer does not take command properly.
 However, if there is antivirus software in your computer system, then it can easily
check programs and files on a system for virus signatures.

13.  Functions slower than normal
 Responds slowly and freezes often
 Restarts itself often
 See uncommon error messages, distorted menus, and dialog
boxes
 Notice applications fail to work correctly
 Fail to print correctly

14. Different virus preventive measures.
Installation of an effective antivirus software.
Patching up the operating system.
Patching up the client software.
Putting highly secured Passwords.
Use of Firewalls.

15.  Following are the Best Antivirus Software of 2023
◦ Bitdefender: Best Overall
◦ Avira: Best Value for Your Money
◦ AVG: Best for Solo Entrepreneurs
◦ McAfee: Best for Multi-Device Protection
◦ Malwarebytes: Best for Real-Time Protection
◦ Avast: Best for Remote Workers
◦ F-Secure: Best for Plan Customization
◦ G DATA: Best for Comprehensive Features
◦ Trend Micro: Best for Phishing Protection
◦ ESET: Best for Technical Users