A computer virus is a malicious program that self-replicates by copying itself to another program. In other words, the computer virus spreads by itself into other executable code or documents. The purpose of creating a computer virus is to infect vulnerable systems, gain admin control and steal user sensitive data. Hackers design computer viruses with malicious intent and prey on online users by tricking them.

One of the ideal methods by which viruses spread is through emails – opening the attachment in the email, visiting an infected website, clicking on an executable file, or viewing an infected advertisement can cause the virus to spread to your system. Besides that, infections also spread while connecting with already infected removable storage devices, such as USB drives.

It is quite easy and simple for the viruses to sneak into a computer by dodging the defense systems. A successful breach can cause serious issues for the user such as infecting other resources or system software, modifying or deleting key functions or applications and copy/delete or encrypt data.

TYPES OF VIRUSES

Boot Sector Virus – This type of virus infects the master boot record and it is challenging and a complex task to remove this virus and often requires the system to be formatted. Mostly it spreads through removable media.

Direct Action Virus – This is also called non-resident virus, it gets installed or stays hidden in the computer memory. It stays attached to the specific type of files that it infect. It does not affect the user experience and system’s performance.

Resident Virus – Unlike direct action viruses, resident viruses get installed on the computer. It is difficult to identify the virus and it is even difficult to remove a resident virus.

Multipartite Virus – This type of virus spreads through multiple ways. It infects both the boot sector and executable files at the same time.

Spacefiller Virus – This is also called “Cavity Viruses”. This is called so as they fill up the empty spaces between the code and hence does not cause any damage to the file.

#File infectors:
Few file infector viruses come attached with program files, such as .com or .exe files. Some file infector viruses infect any program for which execution is requested, including .sys, .ovl, .prg, and .mnu files. Consequently, when the particular program is loaded, the virus is also loaded.

Besides these, the other file infector viruses come as a completely included program or script sent in email attachments.

#Macro viruses:
As the name suggests, the macro viruses particularly target macro language commands in applications like Microsoft Word. The same is implied on other programs too.

In MS Word, the macros are keystrokes that are embedded in the documents or saved sequences for commands. The macro viruses are designed to add their malicious code to the genuine macro sequences in a Word file. However, as the years went by, Microsoft Word witnessed disabling of macros by default in more recent versions. Thus, the cybercriminals started to use social engineering schemes to target users. In the process, they trick the user and enable macros to launch the virus.

Since macro viruses are making a come back in the recent years, Microsoft quickly retaliated by adding a new feature in Office 2016. The feature enables security managers to selectively enable macro use. As a matter of fact, it can be enabled for trusted workflows and blocked if required across the organization.

#Overwrite Viruses:

The virus design purpose tends to vary and Overwrite Viruses are predominantly designed to destroy a file or application’s data. As the name says it all, the virus after attacking the computer starts overwriting files with its own code. Not to be taken lightly, these viruses are more capable of targeting specific files or applications or systematically overwrite all files on an infected device.

On the flipside, the overwrite virus is capable of installing a new code in the files or applications which programs them to spread the virus to additional files, applications, and systems.

#Polymorphic Viruses:
More and more cybercriminals are depending on the polymorphic virus. It is a malware type which has the ability to change or mutate its underlying code without changing its basic functions or features. This helps the virus on a computer or network to evade detection from many antimalware and threat detection products.

Since virus removal programs depend on identifying signatures of malware, these viruses are carefully designed to escape detection and identification. When a security software detects a polymorphic virus, the virus modifies itself thereby, it is no longer detectable using the previous signature.

#Resident Viruses:
The Resident virus implants itself in the memory of a computer. Basically, the original virus program is not required to infect new files or applications. Even when the original virus is deleted, the version stored in memory can be activated. This happens when the computer OS loads certain applications or functions. The resident viruses are troublesome due to the reason they can run unnoticed by antivirus and antimalware software by hiding in the system’s RAM.

#Rootkit Viruses:
The rootkit virus is a malware type which secretly installs an illegal rootkit on an infected system. This opens the door for attackers and gives them full control of the system. The attacker will be able to fundamentally modify or disable functions and programs. Like other sophisticated viruses, the rootkit virus is also created to bypass antivirus software. The latest versions of major antivirus and antimalware programs include rootkit scanning.

#System or Boot-record Infectors:

The Boot-record Infectors infect executable code found in specific system areas on a disk. As the name implies, they attach to the USB thumb drives and DOS boot sector on diskettes or the Master Boot Record on hard disks. Boot viruses are no more common these days as the latest devices rely less on physical storage media.

How to Remove Virus Using CMD

Now, follow the steps below to delete viruses from your computer or storage device using CMD.

Step 1. Type cmd in the search bar, right-click “Command Prompt” and choose “Run as an administrator”.

Step 2. Type F: and press “Enter”. (Replace “F” with the drive letter of the infected partition or device.)

Step 3. Type attrib -s -h -r /s /d *.* and hit “Enter”.

Step 4. Type dir and hit “Enter”. Now you will see all the files under the assigned drive. (The dir command displays a list of a directory’s files and subdirectories.)

Step 5. For your information, a virus name may contain words like “autorun” and with “.inf” as the extension. Thus, if you find such suspicious files, type del autorun.inf to remove the virus.

Here are the basic attributes of the ‘attrib’ command:

R – represents the “Read-only” attribute of a file or folder. Read-only means the file cannot be written on or executed.
H – the “Hidden” attribute.
A – stands for “Archiving” which prepares a file for archiving.
S – the “System” attribute changes the selected files or folders from user files into system files.
I – “not content indexed file” attribute.

The “attrib” Syntax:

ATTRIB [+ attribute | – attribute] [pathname] [/S [/D]]

In the above command, let’s see what the different parameters and switches are:

‘+ / –’: To enact or to cancel the specified attribute.
‘attribute’: As explained above.
‘/S’: Searching throughout the entire path including subfolders.
‘/D’:  Include any process folder.
‘pathname’: Path where the target file or folder is located.

Here is the proper syntax order for attrib command:

ATTRIB [+R | -R] [+A | -A ] [+S | -S] [+H | -H] [+I | -I] [drive:][path][filename] [/S [/D] [/L]]Warning Be careful while using the Command Prompt. Improper use of cmd can result in system damage.

If you receive the message “Access denied”, you should:

• Make sure you have run Command Prompt as an administrator
• Make sure the file/folder is not in use
• Check the permission of the current account and make sure you have full control over the file/folder (right-click the file/folder/partition and go to “Security”)
• Use CHKDSK command to check for file system errors (run Command prompt and enter chkdsk /f [drive letter]:)

Manual input of the command line is suitable for computer professionals since wrong commands can cause more severe problems. Therefore, for security and usability, we strongly recommend you try an automatic command line alternative.

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