What is a computer virus?

A computer virus is a self-replicating malicious code or program designed to do damage. Learn about the impact and what you can do to protect your business.

Illustration of computer virus
Illustration of computer virus

A computer virus is a variety of malicious code or program crafted to alter normal computer operations and spread through self-replication. The virus attaches to a program or file, lying in wait until you run the infected source, thereby executing the malicious code.

From there, the computer virus may steal passwords, log keystrokes, spam email contacts, corrupt or destroy data, damage programs, reformat the hard drive, and/or slow normal functions. 

In short, a computer virus acts much like any other virus. It does damage. It spreads from host to host. And its villainous rampage must be stopped in order to return to normalcy.

We’ll explain what you should know about computer viruses, how they impact businesses, and what you can do to prevent and detect them.

What is the difference between a computer virus and malware?

A computer virus is a type of malware, but not all malware qualifies as a computer virus. The term malware encompasses any and all malicious software. However, for malware to be considered a virus, it must insert itself into another program and self-replicate. 

Other types of malware can be just as devastating as viruses. We’ll break down some of the most common variations. 

Types of malware

  • Virus: A computer virus inserts code into an application, program, file, or system and spreads copies of itself when triggered.

  • Fileless malware: Fileless malware alters files native to the operating system to appear legitimate and evade detection. 

  • Rootkit: A rootkit is a clandestine malicious program that gives threat actors a backdoor into your computer. 

  • Trojan: A Trojan, also known as a Trojan horse, is malicious software that looks legitimate to trick users into executing it. 

  • Worm: Like viruses, worms are self-replicating malware. However, they’re not dependent on a host, and they don’t need to be triggered by a user action. 

  • Spyware: Keyloggers and other forms of spyware collect activity data, which can be used to steal credentials or collect other sensitive information.

  • Ransomware: Ransomware encrypts files, effectively holding them hostage until a ransom is paid. 

  • Adware: Adware collects personal information and displays unwanted ads. 

Types of Computer Virus

What are the different types of computer viruses?

Hackers utilize a wide array of computer viruses, and new viruses emerge regularly. No one ever said cybersecurity was easy. Let’s bemoan a few common viruses: 

Polymorphic virus: By regularly mutating, these viruses nimbly avoid detection. 

Multipartite virus: This computer virus simultaneously infects the boot sector and files, performing unauthorized actions to spread.

Boot sector virus: Often transmitted via a malicious USB drive, this virus typically targets the Master Boot Record. 

File infector: Also known as a file-infecting virus, a file infector generally attaches to executable files or command extensions.

  • Resident virus: A resident virus lives in your RAM and interferes with your operating system. 

  • Direct action virus: A direct action virus targets a specific file type (usually executable files) and activates when an infected file is opened.

Browser hijacker: As the name suggests, a browser hijacker redirects your browser to malicious websites. 

Web scripting virus: Hiding in the coding of links, images, ads, videos, and websites, a web scripting virus can infect systems through downloads or visits to an infected website.

Network virus: A network virus travels through the network and replicates via network packets.

Macro virus: Often transmitted via an infected Microsoft Word or Excel file, macro viruses are written in the same macro language as the software and frequently spread through email attachments. 

Overwrite virus: This computer virus overwrites file content with its own code to destroy system elements.

Computer virus impact

How do computer viruses impact businesses?

Computer viruses affect businesses in innumerable ways, but they’re particularly damaging to operations, finances, and reputation. 

Interruption of normal operations

A computer virus can bring your day-to-day operations to a grinding halt. Between lost data and disabled computer systems, you may not be able to maintain the consistency your customers and clients rely on. While your IT team scrambles to restore backups, other employees may be left sitting on their hands, unable to perform their jobs without essential resources. 

Financial damage

Calculating the true cost of a computer virus is nearly impossible. That said, there’s no doubt that the financial damage can be devastating. If left unchecked, a virus can lead to a full-scale data breach, which costs an average of $4.24 million per incident.

Many industries are also subject to cybersecurity compliance requirements. Experiencing a cybersecurity incident may point to violations that could result in hefty fines. 

Reputation damage

If a virus infection interrupts normal operations or puts private information at risk, you may have no choice but to disclose it to clients and customers. While cybercriminals may target any business, succumbing to an attack can do irreparable harm to your reputation. With reputation accounting for 63% of a company’s market value, the reputational damage can continue to harm your business for years to come.

Computer virus

How can you prevent computer viruses at your company?

Preventing computer viruses can save your business time, money, and hangover-level headaches. With a few simple techniques, you can dodge those bullets like you’re in “The Matrix.” 

Train employees

All too often, well-meaning employees inadvertently introduce a virus into your environment. Viruses and other malware are frequently transmitted through suspicious links or email attachments. Phishing emails may appear legitimate on the surface, making detection all the more complicated. 

If your employees don’t know what to look for, they may be more susceptible to the tricks of cybercriminals, exposing your business to risk. Equipping your staff with the knowledge and skills to recognize the early signs of an attack attempt turns them into your first line of defense. 

Use a firewall

A firewall is like the drawbridge of a castle. If the king’s friends arrive for mead and merriment, the castle guards lower the drawbridge to let them in. But if a band of well-armed barbarians shows up, you better bet that drawbridge is staying as closed as a Blockbuster store.

Similarly, a firewall blocks your internal business network from unwelcome external users, blocks access to unapproved websites, and blocks malicious applications. Some things may still sneak through, but a good firewall makes a cybercriminal’s job much more complicated. 

Install antivirus software

When malware makes it past the firewall, antivirus software lies in wait to intercept it. Virus protection software is designed to detect and remove several varieties of malware, including viruses, Trojans, rootkits, spyware, and more. 

Deploy updates and patches quickly

Updates and patches address newly discovered vulnerabilities that cybercriminals look to exploit. When developers announce a new patch or update, savvy threat actors often act quickly to take advantage before businesses have time to protect themselves. In fact, a study by Ponemon Institute and ServiceNow found that 60% of breaches occurred due to an unpatched known vulnerability. Rapid deployment can be a gamechanger in keeping your systems safe, which is why PDQ Deploy is a good sidekick for all your quests. It makes deployment quick and painless. 

How can you tell if your network or computer has a virus?

Virus-infected computers typically show telltale symptoms. Recognizing the signs that a device is compromised can help you address the problem more quickly, limiting dwell time. 

Watch for the following indications: 

  • Frequent crashes, blue screens, or error messages

  • Slow performance

  • Unknown programs starting 

  • Unknown apps appearing

  • Popups with links to malicious websites

  • Browser homepage changes

  • Password changes

  • Suspicious messages sent from your account

  • Computer fan runs more often

  • Antivirus software and/or firewalls malfunction

If you’ve noticed any of these signs that your computer may be infected, contact your company’s IT department to detect and remove the virus. 

How can you detect computer viruses?

A virus scanner or a threat detection service can help you pinpoint viruses in your environment. 

Scanners are a critical component of antivirus software. They check your memory, boot sector, and disk for potential signs of viruses. Should the scanner find a suspected virus, it will quarantine it, delete it, or disinfect it. 

Threat detection services typically take it a step further by leveraging human expertise and analytics to identify more advanced threats. 

Virus scanners and threat detection services can use several types of detection methods: 

  • Signature-based detection: Looks for digital fingerprints consistent with the patterns of known attacks

  • Behavioral detection: Uncovers unknown threats by evaluating code to analyze its potential actions

  • Cloud-based detection: Maintains threat definitions in the cloud to free up space and provide real-time protection against the latest threats

Hand on laptop with cybersecurity

How do you choose the right antivirus software for your business?

Selecting the right antivirus software for your business requires weighing your needs against the software’s features. There are countless quality options on the market, and each carries distinct potential benefits and drawbacks. 

Questions to consider

Asking yourself the following questions can help you narrow down your choices for antivirus software: 

  • What devices and operating systems does it support?

  • What features do you really need?

  • How many devices do you need to protect?

  • How much does it cost?

  • Is there after-sales support?

Antivirus software features 

Antivirus software solutions have features intended to enhance your overall cybersecurity posture. However, some components can increase the cost without necessarily improving the value for your business. Understanding the standard features of antivirus software makes it easier to weigh what your company truly needs. 

Prevention & Detection

Prevention and detection are at the heart of all antivirus software solutions. They aim to stop viruses from infecting your computer and detect those already in your environment for rapid remediation. Key features that work towards these goals include:  

  • Reactive file scanning: Scans each file to evaluate risks before opening or downloading it

  • System scanning: Scans the full device for signs of compromise

  • Real-time scanning: Provides protection as you use the computer

  • Web browsing protection: Scans URLs and web pages and let you know whether they’re safe to visit

  • Firewalls: Filters network traffic  

  • Vulnerability detection: Scans for known exploitable vulnerabilities

  • Scan scheduling: Performs routine scans on your schedule

  • Spam & anti-phishing protection: Identifies emails that may contain malicious attachments and URLs


Once it detects a virus, the antivirus software should be able to stop it from damaging your computer. Common removal methods include: 

  • Quarantining: Moves potentially malicious files to a safe folder so that you can review them

  • Auto-cleaning: Cleans infected files automatically

Other features

Antivirus software often comes with additional features. While they may not be essential to prevention, detection, and removal, they can provide added value.

  • Automatic updating: Installs updates automatically to stay current 

  • Data & traffic encryption: Encrypts data and traffic to protect privacy

  • Cloud backup: Copies files to the cloud in case they are lost or stolen 

  • Secure browser: Includes extra security features for safer browsing

  • Secure deletion of files: Removes files and prevents recovery 

  • Password manager: Generates, manages, and stores passwords

  • System optimization: Detects and cleans unnecessary files

  • VPN service: Encrypts data and hides your activity

  • Data leak monitoring: Notifies you of leaked data 

Features vary between antivirus solutions, but at a bare minimum, you should look for the following: 

  • High-quality known threat database: To protect against the latest threats, antivirus software needs a comprehensive and current known threat database. Without it, your environment may not be as secure as you think.

  • Good detection rates: For a solution to work, it must limit false positives and false negatives. False positives alert to non-malicious activity, wasting time and resources. False negatives can be even more devastating, failing to identify a true threat and leaving you open to a cybersecurity incident. 

  • Runs well without slowing performance: Antivirus software should be able to perform quietly in the background without causing significant lag. 

  • Easy to use: With so many convenient solutions on the market, there’s no need to use a lot of time and effort to operate your antivirus software. An intuitive interface and automatic updates make antivirus software easier to use. 

Woman on Laptop

How do you deal with computer viruses?

Once you realize you may have a computer virus, you should aim to remove it as quickly as possible to limit the amount of time that threat actors have in your environment. If you’re using a PC, these 10 easy steps usually nip the virus in the bud. 

1. Get high-quality paid antivirus software

While free options are widely available, paid software typically has more robust features. Ideally, you should use a paid solution at all times, but it is especially important to invest in quality if you suspect you already have a virus in your computer system.

2. Disconnect from the internet

Since some computer viruses use your internet connection to proliferate, you may want to disconnect the affected machine from the internet to protect other connected devices. 

3. Reboot in safe mode

Using safe mode helps protect your device while you battle the virus. 

If your operating system is Microsoft Windows 8.1 or later, follow these steps: 

  • Click the start button, then the power icon

  • Hold down the shift key, and press “Restart” 

  • Select “Troubleshoot,” then “Advanced Options,” then “Startup Settings”

  • Click “Restart”

  • Your computer will restart and show you a “Startup Settings” menu; select “Enable Safe Mode with Networking” 

4. Delete temporary files

Since some viruses launch when your computer boots, delete temporary internet files as a precaution. 

To do this: 

  • Type “Disk Cleanup” in the Windows search bar and open the app

  • Check “Temporary internet files” and “Temporary files”

  • Click “Clean up system files”

5. Run a full system scan

Using your high-quality, paid antivirus software, run a full system scan. This may take several hours.

6. Delete or quarantine any detected virus

Once the scan is complete, delete or quarantine malicious files.

7. Rescan your computer

After removing any threats detected in the initial scan, scan again to confirm that the malware was successfully removed and that there are no lingering remnants of virus code. 

8. Reboot your computer

With the virus removed, reboot your computer out of safe mode.

9. Change passwords

When the virus was on your computer, passwords may have been compromised. To be safe, change any important passwords. If you prefer to skip this step, check the virus’s functionality through the antivirus software page or the technical support team. If you can confirm it didn’t collect credentials or log keystrokes, changing passwords may be unnecessary.

10. Update software

Update and patch all software and apps on your computer, including the operating system and browser. This helps address known vulnerabilities to prevent threat actors from infiltrating your environment. Continue to update regularly for a better overall cybersecurity posture. 

Every day, computer viruses devastate businesses. And all too often, they’re preventable. Keeping your machines up to date is one of the easiest ways to reduce the risk of a virus hurting your business’s bottom line and reputation. 

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