A computer virus is a type of malicious software that spreads from one system to another. It attaches itself to files, programs, or parts of the operating system and performs harmful actions. Some viruses delete files, some slow down the computer, while others steal sensitive information.
Also Read: Examples of Computer Viruses
Characteristics of Computer Virus
Computer viruses have specific characteristics that make them dangerous:
- Self-Replication: A virus makes copies of itself. It spreads to different locations on the same computer or to other computers.
- Infection: A virus attaches itself to files, programs, or even parts of the operating system.
- Activation: A virus activates when a user opens an infected file or runs an infected program.
- Harmful Effects: A virus can delete files, steal information, slow down the system, or crash the computer.
Types of Computer Viruses
Here are some common types of Computer Viruses:
1. Boot Sector Virus
A boot sector virus infects the boot sector of the hard drive or removable storage devices. It activates when the computer starts up. These viruses can be very difficult to remove because they infect the system’s startup files.
They can spread through infected USB drives, CDs, or network connections. Once the virus infects the boot sector, it loads before the operating system, making it hard to detect and remove.
2. File Infector Virus
A file infector virus attaches itself to executable files such as programs with extensions like .exe or .com. When the user runs an infected program, the virus spreads to other files on the system.
Some file infector viruses only damage specific programs, while others affect multiple applications. These viruses are often spread through software downloads and email attachments.
3. Macro Virus
A macro virus infects documents and spreadsheets that use macros, such as Microsoft Word or Excel files. It spreads when users open infected documents. These viruses are often sent as email attachments or downloaded from untrusted websites. Macro viruses can delete data, change document content, or execute harmful scripts.
4. Polymorphic Virus
A polymorphic virus changes its code every time it replicates. This makes it difficult for antivirus software to detect. These viruses are very advanced and often used in cyberattacks. Since their code keeps changing, traditional virus detection methods struggle to identify them. They can cause serious damage to computer systems by modifying files and stealing information.
5. Resident Virus
A resident virus hides in the computer’s memory (RAM). Even if the infected program is deleted, the virus remains active. It continues to spread and infect other files. These viruses are dangerous because they do not need the original host file to function. They can slow down the system, corrupt files, and cause unexpected crashes.
How Computer Viruses Spread
Computer viruses spread in different ways. Some include:
1. Downloading Infected Files
One of the most common ways a virus spreads is through downloading infected files. Many free software programs, cracked versions of paid software, and unverified files from unknown sources contain viruses. When users download and install such files, the virus gets inside the computer.
2. Opening Malicious Email Attachments
Hackers often send emails that look like they are from trusted companies, friends, or banks. These emails may contain an attachment, such as a PDF, document, or ZIP file, that is infected with a virus.
When users open the attachment, the virus runs and spreads inside the system. Some emails also contain links that direct users to fake websites where viruses are automatically downloaded.
3. Using Infected USB Drives
USB drives and external storage devices are common tools for transferring files, but they can also carry viruses. When a USB drive is plugged into an infected computer, the virus copies itself onto the USB.
If the same USB is then plugged into another computer, the virus spreads to that system as well. Some viruses install themselves automatically without requiring the user to open any files.
4. Clicking on Suspicious Links
Clicking on random links, especially from unknown sources can lead to virus infections. Many hackers use fake ads, pop-up messages, or social media scams to trick users into clicking harmful links. These links may redirect users to websites that automatically download viruses in the background.
5. Visiting Untrusted Websites
Some websites are designed to distribute viruses. These include sites offering pirated software, illegal movie downloads, free games, or hacking tools. When users visit these websites, viruses may be downloaded automatically without their knowledge. Some websites also use malicious pop-up ads that install viruses when clicked.
Symptoms of Computer Virus
A computer infected with a virus may show the following signs:
1. Slow System Performance
One of the first signs of a virus infection is a noticeable decrease in system speed. The computer takes longer to start up, and programs take more time to open or respond. Some viruses use a large amount of RAM and CPU power, making the system slow and unresponsive.
2. Frequent Crashes and Errors
A virus-infected computer may crash unexpectedly or display frequent error messages. Programs might close on their own without warning, and the system may restart suddenly. Some viruses corrupt system files, leading to errors during startup or while running applications.
If a computer crashes repeatedly despite being in good condition, it may be infected with a virus.
3. Unwanted Pop-ups and Ads
If a computer starts showing random pop-up ads, even when no internet browser is open, it is a strong sign of a virus or malware infection. These pop-ups often advertise fake products, security warnings, or software updates to trick users into clicking on them. Some viruses install adware, which continuously displays unwanted ads, slowing down the system.
4. Unauthorized Data Access
Some viruses allow hackers to gain access to personal data. Users may notice that files have been moved, copied, or deleted without their knowledge. In some cases, saved passwords, banking details, or personal documents might be compromised.
Certain viruses, known as spyware, run secretly in the background and track user activity, including keystrokes and login details.
How to Protect a Computer from Viruses?
Preventing viruses is important for keeping computers safe. Here are some ways to protect a system:
- Install Antivirus Software: Antivirus programs scan and remove viruses before they cause harm.
- Avoid Downloading from Unknown Sources: Only download files from trusted websites.
- Do Not Open Suspicious Emails: Hackers often use email attachments to spread viruses.
- Keep Software and Operating System Updated: Updates fix security weaknesses that viruses exploit.
- Use Strong Passwords: A strong password prevents unauthorized access to the system.
