Home / Hacking School / Hacking Class 16 – Introduction to Viruses, Backdoors, Trojans (continued)

Hacking Class 16 – Introduction to Viruses, Backdoors, Trojans (continued)

In the Previous Class We have studied about what are viruses and How they Work and who creates them…Today we are Going in more details about viruses,worms, Trojans etc..So Guys Read On…

Hey guys below I have mentioned some symptoms that will indicate that your system is infected from viruses..

If the system acts in an unprecedented manner, you can suspect a virus attack that is Processes take more resources and are time consuming than previous i.e System hangs frequently…
Some More are mentioned Below:

– If computer beeps with no display
– If one out of two anti-virus programs report virus on the system
– If the label of the hard drive change
– Your computer freezes frequently or encounters errors
– Your computer slows down when programs are started
– You are unable to load the operating system
– Files and folders are suddenly missing or their content changes
– Your hard drive is accessed too often (the light on your main unit flashes rapidly)
– Microsoft Internet Explorer “freezes” 
– Your friends mention that they have received messages from you but you never sent such messages 


Most of us thinks that worms are viruses and their working is similar to viruses but this not the real scenario. There is a Big difference between the general viruses and Worms.

A worm is a special type of virus that can replicate itself and use memory, but cannot attach itself to other programs. A worm spreads through the infected network automatically but a virus does not.
How To Detect Your System is Infected by Virus??

This is one of the major question to answer and the simplest answer to it is that there are some General Indications that Indicates that System is infected or Not.
General Indications are stated Below:

•Programs take longer to load than normal(because virus halts the normal working of programs as it attaches itself to it, so the execution time increases) .
•Computer’s hard drive constantly runs out of free space.
•Files have strange names which are not recognizable.
•Programs act erratically(Programs Gives errors on use)
•Resources are used up easily (can be Easily viewed using task manager).

Viruses infect the system in the following ways:
1.Loads itself into memory and checks for executables on the disk.
2.Appends the malicious code to a legitimate program which is Important to the user.
3.Since the user is unaware of the replacement, he/she launches the infected program.
4.As a result of the infected program being executes, other programs get infected as well.
5.The above cycle continues until the user realizes the anomaly within the system.


Hacking Class 16 - Introduction to Viruses, Backdoors, Trojans (continued)

The life cycle indicated above is a general life cycle of the Virus from design Phase to Elimination phase…
Viruses are classified on the basis of two basic Things:
1. What they Infect
2. How they Infect

System Sector or Boot Virus:
•Infects disk boot sectors and records.

File Virus:
•Infects executables in OS file system.

Macro Virus:
•Infects documents, spreadsheets and databases such as word, excel and access.
Source Code Virus:
•Overwrites or appends host code by adding Trojan code in it.

Network Virus:
•Spreads itself via email by using command and protocols of computer network.

Thats all for Today we will discuss more about viruses in the Next tutorial…So guys Keep Reading …If You have any Queries ask me.. In the Next class we will discuss more about specific types of viruses and much more.. So Keep Enjoying..

About Lokesh Singh

Hello Friends, i am Lokesh Singh, certified Ethical hacker ( CEH, SSA, CSIF , CISSP). Have 8+ years of extensive experience in Ethical Hacking, Cyber Security and Penetration Testing domain.


  1. dude he might have said it by mistake….just chilll…i can c u r a hacker…..

  2. whose the Mam here lol… I am Damn Hacker…And Owner of this website..

  3. really good thx man!

  4. really good one

  5. really a helpful lesson ,,,,keep it going

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