Prerequisite

In taking this course, it is expected that you should have understood and can answer the question, what is a computer? If not, click here.

What are Computer Viruses?

Computer viruses aim to disrupt systems, cause major operational issues, and result in data loss and leakage. A key thing to know about computer viruses is that they are designed to spread across programs and systems. Computer viruses typically attach to an executable host file, which results in their viral codes executing when a file is opened. The code then spreads from the document or software it is attached to via networks, drives, file-sharing programs, or infected email attachments.

A computer virus is a type of malicious software, or malware, that spreads between computers and causes damage to data and software.

Common Signs of Computer Viruses

A computer virus will more than likely have an adverse effect on the device it resides on and may be discoverable through common signs, such as:

• Slowing down of the computer: This is in fact, the most common sign of a virus infection on a computer. The speed of the computer appears to slow down from the normal rate of operation, symptoms like delay in booting, lagging in responding to keyboard inputs, drags of the mouse cursor on the screen, system over heating, and many others begin to occur.

• Pop-up Windows: When an executable virus infects a computer, programs begin to display pop-up windows that may continue replicating until the user is forced to shutdown the computer or end task abruptly.

• Self-executing behaviors from programs: Have you experienced when a software program you are working with, probably Microsoft Word, freezes, or even closes abruptly without you sending a close command? It is very likely that this is a sign that a computer virus has infected that your software program!

• Automatic log-off: Some computer viruses are designed to affect specific applications, which will either cause these applications to crash or force the user to automatically log out of the system.

• Crashing of the Device: System crashes and the computer itself unexpectedly closing down are common indicators of a virus. Computer viruses cause computers to act in a variety of strange ways, which may include opening files by themselves, displaying unusual error messages, or clicking keys at random.

• Mass Messages sent from your account or email: Computer viruses are commonly spread via email. Most often, hackers can use other people's email accounts to spread malware and carry out wider cyberattacks. Therefore, if an email account has sent emails in the outbox that a user did not send, then this could be a sign of a computer virus.

How Do Computer Viruses Attack and Spread?

We can divide the mode of how computer viruses spread and attack into two categories:

Offline mode and Online mode

1. Offline mode: In the early days of computers, viruses were spread between devices using floppy disks. Nowadays, viruses can still be spread via hard disks and Universal Serial Bus (USB) devices, but they are more likely to be passed between devices through the internet.

2. Online mode: Computer viruses can be spread via email, with some even capable of hijacking email software to spread themselves. Others may attach to legitimate software, within software packs, or infect code, and other viruses can be downloaded from compromised application stores and infected code repositories.

A key feature of any computer virus is it requires a victim to execute its code or payload, which means the host application should be running.

Types of Computer Viruses

There are several types of computer viruses that can infect devices.

1. Resident Virus: Resident Viruses propagate themselves by infecting applications on a host computer. A resident virus achieves this by infecting applications as they are opened by a user. A non-resident virus is capable of infecting executable files when programs are not running.

2. Multipartite Virus: A multipartite virus uses multiple methods to infect and spread across computers. It will typically remain in the computer’s memory to infect the hard disk, then spread through and infect more drives by altering the content of applications. This results in performance lag and application memory running low. Multipartite viruses can be avoided by not opening attachments from untrusted sources and by installing trusted antivirus software. It can also be prevented by cleaning the boot sector and the computer’s entire disk (complete formatting).

3. Direct Action Viruses: A direct action virus accesses a computer’s main memory and infects all programs, files, and folders located in the autoexec.bat path, before deleting itself. This virus typically alters the performance of a system but is capable of destroying all data on the computer’s hard disk and any USB device (i.e. flash drives, phones) attached to it. Direct action viruses can be avoided through the use of antivirus scanners. They are easy to detect, as it is in restoring infected files.

4. Browser Hijacker: A browser hijacker manually changes the settings of web browsers, such as replacing the homepage, editing the new tab page, and changing the default search engine. Technically, it is not a virus because it cannot infect files but can be hugely damaging to computer users, especially to those who will not be able to restore their homepage or search engine. It can also contain adware (addons and plugins) that causes unwanted pop-ups and advertisements. Browser hijackers typically attach to free software and malicious applications from unverified websites or app stores, so only use trusted software and reliable antivirus software.

5. Overwrite Virus: Overwrite viruses are extremely dangerous. They can delete data and replace it with their own file content or code. Once files get infected, they cannot be replaced, and the virus can affect Windows, DOS, Linux, and Apple systems. The only way this virus can be removed is by deleting all of the files it has infected, which could be devastating. The best way to protect against the overwrite virus is to use a trusted antivirus solution and keep it updated.

6. Web Scripting Virus: A web scripting virus attacks web browser security, enabling a hacker to inject web-pages with malicious code, or client-side scripting. This allows cyber criminals to attack major websites, such as social networking sites, email providers, and any site that enables user input or reviews. Attackers can use the virus to send spam, commit fraudulent activity, and damage server files. Protecting against web scripting is reliant on deploying real-time web browser protection software, using cookie security, disabling scripts, and using malicious software removal tools.

7. File Infector: A file infector is one of the most common computer viruses. It overwrites files when they are opened and can quickly spread across systems and networks. It largely affects files with .exe or .com extensions. The best way to avoid file infector viruses is to only download official software and deploy an antivirus solution.

8. Network Virus: Network viruses are extremely dangerous because they can completely cripple entire computer networks. They are often difficult to discover, as the virus could be hidden within any computer on an infected network. These viruses can easily replicate and spread by using the internet to transfer to devices connected to the network. Trusted, robust antivirus solutions and advanced firewalls are crucial to protecting against network viruses.

9. Boot Sector Virus: A boot sector virus targets a computer’s master boot record (MBR). The virus injects its code into a hard disk’s partition table, then moves into the main memory when a computer restarts. The presence of the virus is signified by boot-up problems, poor system performance, and the hard disk becoming unable to locate. Most modern computers come with boot sector safeguards that restrict the potential of this type of virus. Steps to protecting against a boot sector virus include ensuring disks are write-protected and not starting up a computer with untrusted external drives connected.

Frequently asked Questions about Viruses

• Is Trojan a Virus? A Trojan horse is a type of program that pretends to be something it is not to get onto a device and infect it with malware. Therefore, a Trojan horse virus is a virus disguised to look like something it is not. For example, viruses can be hidden within unofficial games, applications, file-sharing sites, and bootlegged movies.

• Is a Worm a Virus? A computer worm is not a virus. Worms do not need a host system and can spread between systems and networks without user action, whereas a virus requires users to execute its code.

• Is Ransomware a Virus? Ransomware is when attackers lock victims out of their system or files and demand a ransom to unlock access. Viruses can be used to carry out ransomware attacks.

• Is Rootkit a Virus? A rootkit is not a virus. Rootkits are software packages that give attackers access to systems. They cannot self-replicate or spread across systems.

• Is a Software Bug a Virus? "Bug" is a common word used to describe problems with computers, but a software bug is not a virus. A bug is a flaw or mistake in software code, which hackers can exploit to launch a cyberattack or spread malware.

How To Prevent Your Computer From Viruses

There are several ways to protect your computer from viruses. These includes:

• Use Trusted Antivirus Product: Trusted computer antivirus products are crucial to stop malware attacks and prevent computers from being infected with viruses. These antivirus concepts will protect devices from being infected through regular scans and identifying and blocking malware.

• Avoid Clicking Pop-up Advertisements: Unwanted advertisements pop-up are more than likely to be linked to computer viruses and malware. Never click on pop-up advertisements because this can lead to inadvertently downloading viruses onto a computer.

• Scan Email Attachments: A popular way to protect your device from computer viruses is to avoid suspicious email attachments, which are commonly used to spread malware. Computer antivirus solutions can be used to scan email attachments for potential viruses.

• Scan the Files That You Download Using File-sharing Programs File-sharing programs, particularly unofficial sites, are also popular resources for attackers to spread computer viruses. Avoid downloading applications, games, or software from unofficial sites, and always scan files that have been downloaded from any file-sharing program.

• Have a reliable IT Consultant that you can reach out to. That's why you need Appheart Repairs & Solutions to for IT repairs and assistance. Reach out on Whatsapp

References

Original file was posted here: fortinet.com/resources/cyberglossary/comput..

Acknowledgement

Dev P Academy.

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