So, what is a computer virus? It is a program or code designed to sabotage computers and spread amongst them. It mainly results in a loss of performance. Processing may start working slowly, spam of many pop-up windows, entire devices may crash, etc. They used to spread through devices like floppy disks, but nowadays, they spread through USB devices and the internet. There are multiple types of viruses these days designed specially to damage computers or steal data. These are not biological viruses. 

How to identify computer viruses

• Too many pop-up windows on screen – When unusual or unexpected dialogue boxes and windows pop up, those are some signs that the computer has been infected. Fake windows warning could also be a part of the virus which always nudges you to open some specific link or dial a number for help. Legit software from windows will never ask to call any number. That’s how you check if the pop-up is legit or not.
• Random sounds – When you hear windows tones but not any pop up on the screen, it may be because of the infection because the computers are programmed in such a way so that they respond with sounds. It will probably be like warning beeps or chimes or bells.
• Missing Files – When you can observe some change in your files or find some files missing from your computer or even some new files that you did not create, there is a greater chance of viruses.
• Processes may work slowly- When you notice some major lack of performance in your computer without any reasonable explanation, there is a high chance that the computer has been infected by some kind of virus causing the performance issues.
• Random Connection to unknown sites  – When your computer starts connecting to unknown sites by itself, it may have been affected by some kind of virus. A computer needs someone to do the tasks, and if you weren’t the one initiating it, there must be inappropriate software on your computer.

Characteristics of Different Types of Computer Viruses Used for its Identification are:

• Boot Sector Virus: Boot sector viruses infect the boot sector of a disk. These viruses give the appearance that a disk has been physically damaged, but are in fact only infected with a virus.
• File Virus: File viruses are executed when an infected program is run; this can be done manually by running the program or via an autorun feature of Windows OS which automatically executes programs on insertion of a CD-ROM or USB.
• Multipartite Virus: Multipartite viruses are able to infect multiple locations on a host computer. These viruses may infect the Master Boot Record, certain files and/or directories, or even the entire hard drive.
• Polymorphic Virus: The ability to mutate while retaining functionality is an advanced characteristic of a polymorphic virus. During its execution, parts of the virus code will be changed every time it infects a new file, making it difficult to create signatures that can reliably detect it. 
• Encryption-Based Virus: Encryption-based viruses use strong encryption to prevent detection, as well as change the file’s data.
• Encrypted Interchange Format: Encrypted interchange formats are encrypted by malicious software and sent to email addresses or web addresses. Once received by a recipient, the virus is executed.
• Infectious Data Stream: A data stream infection occurs when a stream of infected content is sent from one device to another over a network connection.
• Boot Sector Hoax viruses: hoax viruses are fake viruses used by antivirus companies to raise awareness about the threats posed by computer viruses.

Ways to Prevent Your Computer From Viruses

• By using trusted antivirus software, we can keep our computers safe. They can stop malware attacks and prevent computers from getting infected by a virus. Also, make sure that the software is updated time by time. 
• By scanning our email attachments. It is a really popular way to protect the computer as there are many dangerous viruses ready to corrupt our data in our mails from unidentified sources. We should never open any link or attachment as they could be carrying malware.
• By avoiding clicking on pop-up advertisements, they could lead us to some harmful sites with malware. Once we click on the pop-up, it automatically initiates the download of the virus.   
• By backing up the important data using an external hard drive or in cloud space so that even in case of any malware attack on the computer, the data remains safe.

Conclusion

A computer virus is harmful to computers. There are many kinds of viruses out there and we need to be careful and take precautions to keep the data safe. These viruses could attack our systems and might affect their processing speed, steal the data, add harmful codes to the computer, and whatnot. We can keep our computers safe by backing up the data, avoiding opening suspicious links and sites, or using proper antivirus software. But if unknown sites start opening up there, if there are any missing files or new unexplainable files which you didn’t put up there could be a virus, etc.