Computer virus: types, symptoms, protection and removal
On this page, you will learn everything you need to know about the types, symptoms, protection, prevention, detection and removal of computer viruses.
This article is the result of several well-known sources.
- What is a computer virus?
- Computer virus types
- Computer virus symptoms (signs)
- Computer virus prevention tips
- Computer virus protection
- Computer virus detection and removal
- Related articles
What is a computer virus?
A computer virus is a type of malware (malicious software or code) that is designed to spread from computer to computer and perform harmful activities such as corrupting and disrupting systems or destroying data. (1)
Computer viruses can also copy (duplicate) themselves.
Computer virus types
A list of well-known computer virus types:
- Memory Resident Virus (2) - stays in memory after it executes and after its host program is terminated. In contrast, non-memory-resident viruses only are activated when an infected application runs.
- Overwriting Virus (3) - will copy its own code over the host computer system's file data, which destroys the original program.
- Direct Action Virus (4) - is considered to be “non-resident” and functions by selecting one or more files to infect each time the code is executed. The primary intentions of this virus is copying itself and to spread infection whenever the code is executed.
- Boot Sector Virus (5) - infects computer systems by copying code either to the boot sector on a floppy disk or the partition table on a hard drive. During startup, the virus is loaded into memory. Once in memory, the virus will infect any non-infected disks accessed by the system.
- Cluster Virus (6) - associates itself with the execution of programs by modifying directory table entries to ensure the virus itself will start when any program on the computer system is started. If infected by this virus it will look like every program on your PC is infected; however, this virus is only in one place on the system.
- Macro Virus (7) - is written in a macro language and infects Microsoft Word or similar applications (e.g., word processors and spreadsheet applications) and causes a sequence of actions to be performed automatically when the application is started or something else triggers it.
Computer virus symptoms (signs)
A few computer virus symptoms are:
- Computer and/or internet suddenly slower
- Computer behaves weird
- PC freezes and crashes a lot
- Unusual error messages appear
- Files have been automatically deleted or added
- Unwanted advertisements appear
- Emails have been sent from your account to your contacts (which you know you didn't sent)
- Sudden hardware problems (e.g., display acting weird)
- Antivirus software and/or its shields are turned off automatically
- PC automatically restarts (reboots) by itself
Computer virus prevention tips
- Keep your operating system and software always up-to-date
- Use a firewall
- Use antivirus software
- Don't ignore security warnings from Windows or your antivirus software
- Don't install and use pirated software
- If you don't use Java, then remove or disable it
- Don't click on OK, Yes or Run when a pop-up window appears and ask you to install unknown software. Here's one example: “Your windows computer could be at risk! Install this repair tool to protect and clean your system by clicking Secure Now as soon as possible” Don't fall for this trick!
- Before you want to install free software (freeware) first check if its reliable by reading reviews about it
- Always download software from the official link or from a trusted website
- Don't click on a link (in emails or web pages) if you don't trust it.
- Use a secure and safe web browser like Google Chrome or Mozilla Firefox and keep it updated
- When installing software, always pay attention and always read everything clearly before clicking Next, OK, Install, Continue, etc.
- Microsoft recommends that you disable SMB1 on Windows for security reasons.
Computer virus protection
The BEST protection against computer viruses is YOU.
You can have the best protection there is, but even the best antivirus software can fail to detect new malware (e.g., computerviruses, ransomware, spyware, etc.). (8)
Malware threats grow so fast, that antivirus programs take too long to catch up with malware (even the best free or paid ones). (9)
Therefore, the best protection is yourself.
If you do any of the following:
- Ignore Windows and software updates
- Don't use antivirus software
- Use pirated software
- Install free software without checking if it's reliable
- Click on every link you see
- Ignore security warnings from Windows or antivirus software
- Click on buttons in pop-up windows that appear
Then there's a good chance that your PC will get infected one day.
It's recommended to always use an antivirus program on your PC – even when antivirus software can't protect your computer against all viruses.
It's better to have some protection than no protection at all.
You should only use one antivirus program on your computer.
The free antivirus programs I recommend are:
If you need more functions (e.g., multi-layer ransomware protection) and settings, then you can try a paid antivirus program.
Most antivirus companies offer the option to download and try their paid antivirus programs for free for 30 days.
The paid antivirus programs I recommend are:
Free second opinion virus scanners
It's also recommended to use second opinion virus scanners to get more complete detection coverage, because some programs may detect viruses that others might miss.
The free second opinion virus scanners I recommend are:
- Kaspersky Virus Removal Tool
- Malwarebytes (note: to download the free version, you will have to scroll down to the bottom of the page and then click on DOWNLOAD 14 DAY TRIAL. You will get the Premium version for the first 14 days and after the 14 days it will turn into the free version – which is an on-demand malware scanner)
- Zemana Antimalware
- Emsisoft Emergency Kit
- ESET Online Scanner
- Norton Power Eraser
You can use these scanners to scan your PC periodically (e.g., once a week) or when you think your PC is infected.
You can use virus scanners alongside your current antivirus software. This way you get the chance to use other antivirus software on your PC without any problems.
Computer virus detection and removal
I will show you how to detect and how to get rid of a computer virus for free.
The first thing you want to keep in mind when your PC is infected by a computer virus is whether or not you want to clean it. Because sometimes it may be a better idea to back up any data that you might have and reinstall Microsoft Windows or restore a system image backup that's 100% clean.
Well, if your antivirus (antimalware) software detected a computer virus or other malware, then you will never know for sure if that's the only piece of malware that has infected your system.
Malware can nestle itself deeper into your system and hide so that it can't be discovered by your security software and it can also open doors to other malware.
You also may end up with a damaged Windows installation.
Considering time and effort, sometimes it's better to wipe everything and start all over again. But, if you wanted to do that, you probably wouldn't be reading this article, so, follow the steps below.
With the following steps, I assume that you have access to your system or at least can boot Windows into “Safe Mode with Networking”.
If you cannot access your computer then I recommend Kaspersky Rescue Disk (located in the “Free Tools” section).
Once you have the ISO file you can install it on a USB flash drive with the help of a free tool called Rufus and then you can boot from the USB drive and use the rescue disk.
Let's continue with the next step.
Step 1: Find out if your files are affected by Ransomware
If you cannot open some files on your computer or you see files with missing or weird file extensions (e.g., .cry, .crypto, .locked, .kraken, etc.), your system is probably infected by Ransomware.
If your system is infected by Ransomware, the first thing you should do is to check if your files can be decrypted.
But to do this, you first need to find out which Ransomware has infected your PC.
To find out which Ransomware has infected your PC, look at the ransom note, or look at any messages on the screen or look at the encrypted files and the extension they have.
If you cannot find out which Ransomware infected your PC you can visit ID Ransomware by MalwareHunterTeam and upload the ransom note or an encrypted file.
You can also visit a cybersecurity forum like BleepingComputer.
On this forum, you can find a lot of malware analysts that you can talk to.
You can post something in the forums and upload one of your encrypted files.
They might be able to tell you whether or not you can decrypt your files.
You can also download the Bitdefender Ransomware Recognition Tool to find out which ransomware has encrypted your data and then get the appropriate decryption tool if it exists.
You can visit NoMoreRansom.org or the free ransomware decryptors page on Kaspersky.com and check if they have a decryptor tool for the ransomware that infected your PC.
Step 2: Make a backup of your files
If your files were not affected by ransomware or you were able to decrypt your files, then you should make a backup of your files.
You can use a free backup program like AOMEI Backupper Standard or copy your files to a USB flash drive or external hard drive.
Step 3: Disable startup programs in Windows
1. Open Windows Task Manager.
Three ways to open Task Manager:
- Press the [ctrl] + [alt] + [delete] (del) keys on your keyboard and then click on Task Manager.
- Press the [Windows] + [R] keys on your keyboard, type taskmgr and then click on the OK button or press [Enter].
- In Windows 10, you right-click on the taskbar or start menu button and then click on Task Manager.
2. Click on the Startup tab.
Note: if you don't see the Startup tab then click on More details located at the bottom left of the Taskmanager window.
3. Disable everything that you see here, including your antivirus software.
To do this, right-click on the program and then click on Disable.
Step 4: Disable services in Windows
1. Open Windows System Configuration.
Three ways to open System Configuration:
- Press the [Windows] + [R] on your keyboard, type msconfig and press [Enter].
- Search for msconfig using the Windows search box and then click on System Configuration when it appears.
- Click on the start menu button, click on Windows Administrative Tools and then click on System Configuration.
2. Click on the Services tab.
3. Check (select) the Hide all Microsoft services option located below the list.
4. Click on the Disable all button.
5. Click on the Apply button.
6. Click on OK.
7. Click on Restart to restart your computer.
Important! The order of the following steps are very important, so don't do these steps in a different order.
Step 5: Kaspersky Virus Removal Tool
Download and open Kaspersky Virus Removal Tool.
Scan your PC with Kaspersky Virus Removal Tool and follow its instructions if it found something.
Step 6: Malwarebytes
Download, install and open Malwarebytes (note: to download the free version, you will have to scroll down to the bottom of the page and then click on DOWNLOAD 14 DAY TRIAL. You will get the Premium version for the first 14 days and after the 14 days it will turn into the free version – which is an on-demand malware scanner).
Scan your PC with Malwarebytes and follow its instructions if it found something.
Step 7: Zemana
Download, install and open Zemana Antimalware (for the download button of the free version you will have to scroll down to the comparison table).
Scan your PC with Zemana and follow its instructions if it found something.
Step 8: ESET Online Scanner
Download and open ESET Online Scanner.
Enable detection of potentially unwanted applications, scan your PC with ESET Online Scanner and follow its instructions if it found something.
After these steps, your computer should be relatively clean.
If you want to scan your computer with more virus scanners, then you can also try the following virus scanners:
Thank you for reading this article. Hopefully, you learned enough about computer viruses to keep your PC clean and safe. If you want to learn more about computer and Internet security (cybersecurity), then visit this page.
Maybe you're also interested in:
Malware: types, protection, prevention, detection and removal
Important computer and internet security tips
Windows 10 security tips and is Windows Defender good enough?
Wikipedia: Computer virus
Webopedia: Memory resident virus
Webopedia: Overwriting virus
SpamLaws: Direct action virus
Microsoft: Boot sector virus
Webopedia: Cluster virus
TechTarget: Macro virus
LastLineLabs: Antivirus isn't dead, it just can't keep up
GCN: Is antivirus now useless?
YouTube: How to clean an infected computer