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Trojan horses: They are programs that appear to have one function but actually perform another function.Thus, signature of each copy will vary, and a virus scanner will find it difficult to locate it. Damage caused by malicious software o Virus can destroy file allocation tables (FAT) and lead to the corruption of an entire file system, resulting in the need to fully reinstall and reload the system.Parasitic Virus: It attaches itself to executable files and replicates, when the infected program is executed, by finding other files to infect.Polymorphic Virus: Creates copies that are functionally equivalent but have distinctly different bit patterns.Boot Sector Virus: It infects a boot record and spreads when a system is booted from the disk containing the virus.Viruses: They are programs that modify other programs on a computer by inserting copies of themselves.pUY A virus tries to take control of computer system it has infected at the first opportunity; it makes copies of itself and try to carry harmful task written in its program.o Some worms scan for passwords and other loopholes and then send the information back to the attacker.The modern - day Trojan horses resemble a program that the user wishes to run - a game, a spreadsheet, or an editor.While the program appears to be doing what the user wants, it is also doing something else unrelated to its advertised purpose, and without 3%K 8 the user's knowledge.Viruses: o Need to have some host program, (of which they are a part), executed to activate them.Jas!Types of Viruses: 0?1.2.3.4.

Trojan horses: They are programs that appear to have one function but actually perform another function. The modern - day Trojan horses resemble a program that the user wishes to run - a game, a spreadsheet, or an editor. While the program appears to be doing what the user wants, it is also doing something else unrelated to its advertised purpose, and without
3%K 8
the user's knowledge.
Jas!
Viruses: They are programs that modify other programs on a computer by inserting copies of themselves. Viruses:
• Need to have some host program, (of which they are a part), executed to activate them.
• Executes secretly when the host program run.
pUY
A virus tries to take control of computer system it has infected at the first opportunity; it makes copies of itself and try to carry harmful task written in its program. This process can happen so quickly that the user is not even aware of the presence of a virus in his/her computer.
Types of Viruses:
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1. Parasitic Virus: It attaches itself to executable files and replicates, when the infected program is executed, by finding other files to infect.


2. Memory - Resident Virus: stays in main memory as a part of a system program. Then it infects every program that executes.


3. Boot Sector Virus: It infects a boot record and spreads when a system is booted from the disk containing the virus.


4. Polymorphic Virus: Creates copies that are functionally equivalent but have distinctly different bit patterns. Thus, signature of each copy will vary, and a virus scanner will find it difficult to locate it.
   Damage caused by malicious software
   • Virus can destroy file allocation tables (FAT) and lead to the corruption of an entire file system, resulting in the need to fully reinstall and reload the system.
   • Virus can decrease the space on hard disks by duplicating files.
   • Virus can cause the system to hang so that it does not respond to any keyboard or mouse movements.
   • Most worms disrupt services and create system management problems.
   • Some worms scan for passwords and other loopholes and then send the information back to the attacker.