Computer Viruses

Computer Viruses

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.

Types of Computer Viruses
Trojan horse
Worms
Boot virus
Macro virus
Directory virus
Logic bombs
Resident virus


Trojan Horse
A Trojan Horse program has the appearance of having a useful and desired function.
A Trojan Horse neither replicates nor copies itself, but causes damage or compromises the security of the computer.
A Trojan Horse must be sent by someone or carried by another program and may arrive in the form of a joke program or software of some sort.


Computer Worm
A computer worm is a self-replicating computer program.
It uses a network to send copies of itself to other nodes (computers on the network) and it may do so without any user intervention.
It does not need to attach itself to an existing program.

Boot Virus
This type of virus affects the boot sector of a floppy or hard disk.
This is a crucial part of a disk, in which information on the disk itself is stored together with a program that makes it possible to boot (start) the computer from the disk.
These are normally spread by floppy disks.

Macro Virus
Macro viruses are viruses that use another application's macro programming language to distribute themselves.
They infect documents such as MS Word or MS Excel and are typically spread to other similar documents.

Directory Virus
Directory viruses change the paths that indicate the location of a file.

Logic Bombs
Their objective is to destroy data on the computer once certain conditions have been met.
These are viruses which are programmed to initiate at a specific date or when a specific event occurs.
Some examples are a virus which deletes your photos on Halloween, or a virus which deletes a database table if a certain employee gets fired.

Resident Virus
This type of virus is a permanent which dwells in the RAM memory.
From there it can overcome and interrupt all of the operations executed by the system: corrupting files and programs that are opened, closed, copied, renamed etc.


How does Computer Virus Spread?
Computer virus is a program that must be triggered or somehow executed before it can infect your computer system and spread to others.
Computer viruses can be spread via:
Network / Internet
Storage media

What do viruses do to computers?
Computer viruses can:
Damage files
Interfere with computer's operation
Viruses can't do any damage to hardware.
Unexplained messages appear on the screen
Specific files are mysteriously deleted
Unknown files are added to a disk
An entire disk or drive is erased
The keyboard does not work properly
Unexplained modifications are made to data or documents
Application software seems to be changed
Operating system software appears to be modified
Unexplained printing problems occur


How Can You Protect Yourself? 
Install Anti Virus software.
Practice caution when working with files from unknown or questionable sources.
Do not open e-mail attachments if you do not recognize the sender.
Download files only from reputable Internet sites.
Scan your hard drive for viruses monthly.


Symptoms
Computer may shut on and off all of a sudden
A computer may run slower than normal
Programs may crash often
The computer screen may not be visible
Windows may seem to freeze from time to time
Error messages may come up when you start or shut down the computer


Antivirus Software
Antivirus Software is used to prevent, detect, and remove computer viruses, worms, and Trojan horses.
Antivirus basic functions:
Scan your storage media
Remove
Heal / Repair
Quarantine
Update virus definitions


Examples of Antivirus Software
Norton Antivirus
AVG
Kaspersky
Avast!
PC-Cilin
McAffee
Bitdefender

Virus Removal Tools
Virus removal tools are software for removing specific viruses from infected computers.
They are designed to remove specific viruses.
Examples:
-McAfee Stinger
-Microsoft Windows Malicious Software Removal Tool