Explain any 10 Types of computer viruses.
Answers
There are different types of computer viruses that can be categorized according to their origin, spreading capabilities, techniques, operating system, storage location, files they infect and destructive nature.
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1. Boot Sector Virus
Boot Sector virus infects the storage device’s master boot record (MBR). Any media, whether it is bootable or not can trigger this virus. These viruses inject their code to hard disk’s partition table. It then gets into main memory once the computer restarts (boot). Booting problem, unstable system performance and inability to locate hard disk are common issues that may arise after getting infected. However, this virus has become rare since the decline in floppy disks. Modern operating system has inbuilt boot sector safeguard which make difficult to find the MBR.
Can affect: Any file after getting into the main memory
Examples: Form, Disk killer, Stone virus, Polyboot.B
Protection: Make sure that the disk you are using is write protected. Moreover, do not start/restart computer with unknown external disk connected.
2. Direct Action Virus
This virus quickly gets into the main memory, infect all programs/files/folder defined in Autoexec.bat path and then deletes itself. It can also destroy the data present in harddisk or USB attached to the computer. They keep changing their location on every execution and usually found in hard disk’s root directory. In most cases, they don’t delete system files or alter the system’s overall performance.
Can affect: All .exe and .com file extension
Example: VCL.428, created by the Virus Construction Laboratory
Protection: Use antivirus scanner. Direct action virus is easy to detect and all infected files can be restored completely.
3. Overwrite Virus
Overwrite viruses are very dangerous. They have affected a wide range of operating system including Windows, DOS, Macintosh and Linux. These viruses simply delete the data (partially or completely) and replace the old code with their own. They replace file/program content without changing its size. It is easy to detect as the original program stops working. Once the file gets infected, it can’t be restored and you will end up with losing all data.
Can affect: Any file
Examples: Grog.377, Grog.202/456, Way, Loveletter
Protection: The only way to get rid of this virus is to delete all the infected files.
4. Web Scripting Virus
A web scripting virus breaches web browser security and allows attacker to inject client side scripting into the web page. They propagate a bit faster than other usual viruses. It is used to attack large sites like social networking, user review or email. It has potential to send a large amount of spam, fraud activity and damaged data.
Can affect: Any web page by injecting hidden code in header, footer or root access file.
Examples: DDos, JS.fornight
Protection: Use malicious software removal tool in Windows, Disable scripts, Use cookie security or install real time protection software for web browser.
5. Directory Virus
Directory Virus (also known as Cluster virus) infects the file by changing the DOS directory information. In this case, DOS points to the virus code instead of original program. When you run a program, DOS first loads and executes the virus code before running the actual program code. It becomes very difficult to locate the original file after getting infected.
Can affect: The entire program in the directory
Example: Dir-2
Protection: Install the antivirus to relocate the misplaced files.