S ummary N otes

1. Summary Notes TERM TWO BASIC SEVEN 7 ACADEMIC YEAR 2013/2014 Prepared by Sir Lexis Oppong

2. COMPUTER VIRUSES • DEFINITION: • Computer viruses are malicious code written by individuals with the sole aim of disrupting the normal and smooth operations of the software of a computer.

3. The viruses may multiply in your computer, most especially, at the storage devices example, memory, hard disk, floppy disk and compact disk (CD Computer Viruses

4. TYPES OF COMPUTER VIRUSES • Computer viruses can be classified into several different types. • File infecting or Program Viruses: • It infects program files with extensions like .EXE, .COM, .BIN, .DRV and .SYS. Some file viruses just replicate while others destroy the program being used at that time. • Boot Sector Virus: • This infect the master boot record of the hard disk or the floppy drive. • Multipartite Virus: • They infect both files and boot sector of the computer system. • Stealth Viruses: • They are stealth in native and use various methods to hide themselves and to avoid detection. • Polymorphic Viruses: • They are the most difficult virus detect • Macro Viruses: • A macro is an executable program embedded in a word processing documents or other type of file

5. DIAGRAM OF TYPES OF COMPUTER VIRUS

6. Sources of computer viruses • The top sources of virus attacks are highlighted below: • Downloadable Programs • Cracked Software • Email Attachments • Internet • Booting From CD • Downloadable Programs • One of the possible sources of virus attacks is downloadable programs from the web. Unreliable sources and internet newsgroups are one of the main sources of computer virus attacks.

7. Cracked Software • Most people who download cracked and illegal versions of software online are unaware about the reality that they may contain virus sources as well. Such cracked forms of illegal files contain viruses and bugs that are difficult to detect as well as to remove. Cracked Computer Software

8. Email Attachments • Email attachments are one of the other popular sources of computer virus attacks. There exists a possibility that senders of e-mail unknowingly forward virus along with the email attachment. • Internet-Best Possible Source of Viruses E-mail Icons

9. Internet-Best Possible Source of Viruses • Since the internet is a world wide interconnection of computers viruses spread over here quickly. • Downloading software from the internet is an easy way to transfer virus. Internet Pages

10. Removable Storage Media • Storage media such as floppy disks, CDs, external hard disk and USB storage devices can carry viruses when used on computers that are already infected. Removable Storage Media

11. Network • Computers connected to each other on a network can spread virus quickly when on computer if infected. Computer Networks

12. PROBLEMS OF COMPUTER VIRUSES • they are not easy to remove. • they are destructive and obstructive programs. • they replicate themselves, spread themselves and some even disguise as a real program.

13. Symptoms • Speed: your computer system may slow down under the influence of viruses as they consume your system memory for their execution. This means that virus only execute with the help of system memory like RAM (random access memory). • Operation: computer may hang frequently of may display errortic error messages, viruses are capable of colliding two program together (eg Microsoft Word and Corel Draw), thereby creating software (program) conflict making the system to hang.

14. Booting: your computer may suddenly restart at times, may not load properly, in few experience, you may not be able to access your disk drives. • Peripherals: some computer viruses may invade your Device Manager.

15. EFFECTS OF VIRUS ON COMPUTERS • Slows Down Computers • Virus slows down computer since it uses the computer’s memory whilst active. • Loss of Data • Some Viruses corrupt data and render them useless such that that data may have to discarded. • Data Theft • Some type of computer virus such as spyware can steal data and pass it on to a dangerous hands. • System Crash • Computer virus can also lead to a total the total carsh of a computer. In some extreme situations, the computer may refuse to boot properly.

16. PRECAUTION AGAINST VIRUSES • 1. Avoid copying infected files • 2. Desist from images and folder sharing, because it • may contain virus • 3. Update your antivirus software every month avoid pirating software's • 4. Avoid printer sharing • 5. Scan any storage device such as flash drive before making use of it • 6. Avoid online downloading and internet sharing. • 7. Install active antivirus software • 8. Avoid networking and pairing of devices • 9. Avoid files transfer through Bluetooth, infrared or USB

17. PROGRAMS THAT  PREVENT COMPUTER VIRUSES • Antivirus program • Antivirus programs are written to ensure that a computer is protected from viruses and not infected with virus. Hence it is the most effective and major defense against virus. Examples are: • McAfee Virus Scan • Avast Antivirus • Norton AntiVirus • KasperskyAntiVirus • AviraAntiVirus • AVG Antivirus