A computer virus is a type of malicious software, or malware, that spreads between computers and causes damage to data and software. Computer viruses aim to disrupt systems, cause major operational issues, and result in data loss and leakage. 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 piece of code or an executable program that gets downloaded onto your computer through an email, software download, or an outside storage device. It’s a contagious element that can go from computer to computer, causing your device to perform poorly.
Computer viruses are unwanted software programs or pieces of code that interfere with the functioning of the computer. They spread through contaminated files, data, and insecure networks. Once it enters your system, it can replicate to produce copies of itself to spread from one program to another program and from one infected computer to another computer. So, we can say that it is a self-replicating computer program that interferes with the functioning of the computer by infecting files, data, programs, etc.
There are many antiviruses, which are programs that can help you protect your machine from viruses. It scans your system and cleans the viruses detected during the scan. Some of the popular antiviruses include Avast, Quickheal, McAfee, Kaspersky, etc.
Types of Computer viruses
Overwrite Virus
It is the simplest computer virus that overwrites the code of the host computer system’s file with its malicious code. The content of the infected file is replaced partially or completely without changing the size of the file. Thus, it destroys the original program code by overwriting it with its defective code. The infected files must be deleted or replaced with a new copy as this virus cannot be removed or disinfected.
Append Virus
As the name suggests, this virus appends its malicious code to the end of the host program’s file. After that, it alters the file’s header in a way that the file’s header is redirected to the start of the malicious code of the append virus. Thus, this code is executed each time the program runs. However, it does not destroy the host program; rather, it modifies it in a way that it holds the virus code and enables the code to run itself
Macro Virus
Macro virus alters or infects the macros of a document or data file. It is embedded as a macro in a document and adds its codes to the macros of the document. The virus spreads when infected documents or data files are opened on other computers.
It also spreads through software programs, which execute macros such as Ms. Word, and Ms. Excel. Each time a document is opened using these programs, other related documents will also get infected.
The first macro virus, which was named concept, spread through emails with attached Ms. Word documents. It infected MsWord 6.0 and Ms. Word 95 documents, which were saved using Save As option. Fortunately, it did not cause any harm, except for displaying a message on the screen.
Boot Virus
Boot virus or boot sector virus alters the boot sector program stored in the hard disk or any other storage device such as floppy disks. It replaces the boot sector program with its malicious version. It infects the computer only when it is used to boot up the computer. If it enters after the boot-up process, it will not infect the computer. For example, if someone forgets to remove the infected floppy disk when the pc is turned off and then turns on this pc, it runs the infected boot sector program during the booting process.
Usually, it enters your system through corrupt media files, infected storage devices, and insecure computer networks. The spread of this virus is very rare these days due to the decline in the use of floppy disks and the use of boot-sector safeguards in present-day operating systems.
Resident Virus
The resident virus stays permanently in the primary memory (RAM) of the computer. When you start the computer, it becomes active and corrupts the files and programs running on the computer.
Non-resident Virus:
Unlike the resident virus, the non-resident virus does not reside in the memory of a computer. So, it is not executed from the computer’s memory. For example, executable viruses.
Multipartite Virus
The multipartite virus spreads and infects in multiple ways. It infects both the boot sector and the executable files stored on the hard drive simultaneously. When you turn on a computer, the boot sector virus is triggered as it latches on to the hard drive, which has the data for starting up the computer. Once it is triggered, the program files also get infected.
File Infector Virus
It is one of the commonly found computer viruses. It mainly infects the executable files; the files with .com or .exe extensions. The virus becomes active when the infected file is executed. The active virus overwrites the file partially or completely. Thus it may destroy the original file partially or completely.
Computer Worm
A computer worm is similar to a virus but is technically different from the virus. It can replicate and spread like a virus, but unlike viruses, it does not need a host program to spread. Being able to self-replicate can produce multiple copies of itself. It spreads through networks such as an email sent to an infected email id that can infect your system with a computer worm.
Trojan Horse
A trojan horse is a malware like a virus or a worm, but it is technically different from both. It can’t replicate like viruses and worms. Trojan horse hides in a program. Once you install any such program, the trojan horse enters your computer. It can provide unauthorized access to your computer, send your files to other computers, and may delete files or can make other unwanted changes to your computer.
Cavity virus
It is also known as a spacefiller virus. As the name suggests, this virus tends to install itself by occupying the empty sections of a file. It is not easy to detect this virus as it fills the empty spaces without changing the size of the file.
CMOS Virus
It infects the CMOS, which stands for complementary metal-oxide-semiconductor and is a memory chip that contains the system configuration. This virus can erase or reset the system configuration.
Companion Virus
It resides itself in a file whose name is similar to another program file, which is executed normally. When the program file is executed, the virus gets activated and performs malicious steps such as deleting the files on your computer hard drive. Globe virus is the first known companion virus, which was found in 1992.
Encrypted Virus
It encrypts its payload to make its detection more difficult. It comprises two parts: an encrypted virus body and a decryptor, which decrypts the virus when it is executed. After decryption, the virus can execute itself to replicate and become a resident. Furthermore, it is different from the crypto locker, which is a computer virus that encrypts the hard drive data and holds it for ransom.
Executable Virus
It is a non-resident computer virus, which resides in an executable file. Whenever the infected file is executed, it infects the other files.
Polymorphic Virus
It creates thousands of copies itself; in each copy, it changes the sequence and byte values to evade detection by antivirus software. Even the best antiviruses may not be able to detect this virus. Polymorphic viruses affect data types and functions and generally spread through spam, infected sites, and while using other malware.
Rabbit Virus
It is also known as a wabbit, a fork bomb. It is capable of creating new processes, and each new process further creates new processes. This process continues until this virus utilizes all the available resources in the system and the system falls short of resources. It may cause the target system to slow down and crash. For example, it is like an Infinite loop that repeatedly creates processes that consume lots of CPU cycles and operating system resources.
Stealth Virus
It is a hidden computer virus, which specifically attacks operating system processes. It usually hides in partitions, files, or boot sectors and is capable of going unnoticed during antivirus or anti-malware scans, i.e., it can avoid detection intentionally.
Symptoms of a Computer Virus
There are many warning signs or symptoms which show that a computer is infected with a virus, some of which are as follows:
- Slow computer performance: The machine may work slowly, e.g., it will take more time to open or shut down the computer or while opening a file, document, computer application, etc. The operating system and internet speed may get slow.
- Frequent pop-ups: A virus may cause unusual frequent pop-ups on your window.
- Hard Drive issue: The hard drive may exhibit unusual high activity even when it is not in use. It may cause unwanted changes to your hard drive and may freeze or crash this device.
- Frequent crashes: One may experience frequent sudden system crashes while playing games, watching videos, or doing some other work using the infected system. A blue screen appears when it crashes.
- Unknown programs: Unwanted programs may open or start automatically when you start your computer. You can see these programs in your computer’s list of active applications. Sometimes, the window shuts down unexpectedly without any reason.
- Unusual activities: Your machine may perform differently, such as you may not be able to log into your accounts, delete the corrupt files, Blue Screen of Death (BSOD) may appear frequently, and more. Furthermore, the hardware, software, or OS may start malfunctioning leading to crashing the system abruptly.
- Impaired security solutions: Sometimes, security measures are taken by you, such as antivirus may not work smoothly due to a virus attack on your computer.
- Network issue: Sometimes, you experience high network activity even if you are not connected to the internet and vice versa.
- Unnecessary advertisement: We often see advertisements while browsing, but if you see them even when you are not browsing, it may indicate a virus on your computer.
- Display problems: You may experience different colors in your display if your computer is affected by a virus.
- Affected Applications: Some viruses are developed to affect specific applications. Consequently, some applications may not work on your computer if it is infected.
- Blocked by Antivirus Sites: An antivirus site may deny access to a computer that is infected by a virus.
- Dialog Boxes: Many dialog boxes keep appearing suddenly on your screen.
- Printer Issues: A printer attached to an infected computer may print documents without getting any command or in an inappropriate manner.
- Changed Homepage: Your home page may get changed without any effort from your side. For example, you may see a new toolbar on your screen, and you may be redirected to a different web address instead of the page visited by you initially.
- Strange messages: One may see strange messages on a computer screen such as error messages, e.g., “cannot rename “folder” as a folder already exists with this name”
- Email: This worm tried to harvest data from infected machines to launch a string of DDoS attacks, but was relatively easy to remove.
- Yaha: Yet another worm with several variants, thought to be the result of a cyber-war between Pakistan and India.
- Swen: Written in C++, the Swen computer worm disguised itself to look like a 2003 OS update. Its financial cost has been pegged at $10.4 billion, but not reliably.
- Storm Worm: This worm showed up in 2007 and attacked millions of computers with an email about approaching bad weather.
- Tanatos/Bugbear: A 2002 keylogger virus that targeted financial institutions and spread to 150 countries.
- Sircam: A computer worm from 2001 that used counterfeit emails with the subject line, “I send you this file in order to have your advice.”
- Explorezip: This worm used fake emails to spread to every machine on thousands of local networks.
- Melissa: The most dangerous computer virus in 1999, Melissa sent copies of itself that looked like NSFW pics. The U.S. FBI estimated cleanup and repair costs at $80 million.
- Flashback: A Mac-only virus, Flashback infected over 600,000 Macs in 2012 and even infected Apple’s home base in Cupertino, Calif. In 2020, there’s now more malware on Macs than on PCs.
- Conficker: This 2009 virus still infects many legacy systems and could do significant damage if it ever activates.
- Stuxnet: This worm is reported to have destroyed Iranian nuclear centrifuges by sending damaging instructions.
10 worst computer viruses in history
1. Mydoom – $38 billion
2. Sobig – $30 billion
3. Klez – $19.8 billion
4. ILOVEYOU – $15 billion
5. WannaCry – $4 billion
Ransomware strikes again
6. Zeus – $3 billion
7. Code Red – $2.4 billion
8. Slammer – $1.2 billion
9. CryptoLocker – $665 million
10. Sasser – $500 million
How to prevent malware
Since malware is so widespread and hundreds of thousands of new malicious files are reported every day, there’s no single solution that will prevent all malware. For this reason, we recommend using multiple solutions to add more layers of protection to your computers.
Use Software
Here is a list of some malware prevention software we recommend:
- BitDefender – BitDefender is a well-rounded anti-virus solution that is currently protecting over 500 million users worldwide. It offers unparalleled endpoint protection and virus protection. Free BitDefender trial.
- Malwarebytes – The most effective and widely-adopted anti-malware on the market. The scans are thorough and the program prevents you from executing malicious files and visiting malicious websites. Free Malwarebytes trial.
- TitanFile – TitanFile is an easy-to-use, secure file-sharing platform that enables you to send and receive confidential files securely. TitanFile automatically scans the files for malware before they’re downloaded to your computer. Free TitanFile trial.
- Spybots – Effectively protects you from spyware, protecting your private information and other data from being sent to third parties. Get access.
History
The first academic work on the theory of self-replicating computer programs[rx] was done in 1949 by John von Neumann who gave lectures at the University of Illinois about the “Theory and Organization of Complicated Automata”. The work of von Neumann was later published as the “Theory of self-reproducing automata”. In his essay, von Neumann described how a computer program could be designed to reproduce itself.[rx] Von Neumann’s design for a self-reproducing computer program is considered the world’s first computer virus, and he is considered to be the theoretical “father” of computer virology.[rx] In 1972, Veith Risak directly building on von Neumann’s work on self-replication, published his article “Selbstreproduzierende Automaten mit minimaler Informationsübertragung” (Self-reproducing automata with minimal information exchange).[rx] The article describes a fully functional virus written in assembler programming language for a SIEMENS 4004/35 computer system. In 1980 Jürgen Kraus wrote his diplom thesis “Selbstreproduktion bei Programmen” (Self-reproduction of programs) at the University of Dortmund.[rx] In his work, Kraus postulated that computer programs can behave in a way similar to biological viruses.
The Creeper virus was first detected on ARPANET, the forerunner of the Internet, in the early 1970s.[rx] Creeper was an experimental self-replicating program written by Bob Thomas at BBN Technologies in 1971.[rx] Creeper used the ARPANET to infect DEC PDP-10 computers running the TENEX operating system.[rx] Creeper gained access via the ARPANET and copied itself to the remote system where the message, “I’m the creeper, catch me if you can!” was displayed. The Reaper program was created to delete Creeper.[rx]
In 1982, a program called “Elk Cloner” was the first personal computer virus to appear “in the wild”—that is, outside the single computer or computer lab where it was created.[rx] Written in 1981 by Richard Skrenta, a ninth-grader at Mount Lebanon High School near Pittsburgh, it attached itself to the Apple DOS 3.3 operating system and spread via floppy disk.[rx] On its 50th use, the Elk Cloner virus would be activated, infecting the personal computer and displaying a short poem beginning “Elk Cloner: The program with a personality.”
In 1984 Fred Cohen from the University of Southern California wrote his paper “Computer Viruses – Theory and Experiments”.[rx] It was the first paper to explicitly call a self-reproducing program a “virus”, a term introduced by Cohen’s mentor Leonard Adleman. In 1987, Fred Cohen published a demonstration that there is no algorithm that can perfectly detect all possible viruses.[rx] Fred Cohen’s theoretical compression virus[rx] was an example of a virus that was not malicious software (malware), but was putatively benevolent (well-intentioned). However, antivirus professionals do not accept the concept of “benevolent viruses”, as any desired function can be implemented without involving a virus (automatic compression, for instance, is available under Windows at the choice of the user). Any virus will by definition make unauthorized changes to a computer, which is undesirable even if no damage is done or intended. The first page of Dr. Solomon’s Virus Encyclopaedia explains the undesirability of viruses, even those that do nothing but reproduce.[rx][rx]
An article that describes “useful virus functionalities” was published by J. B. Gunn under the title “Use of virus functions to provide a virtual APL interpreter under user control” in 1984.[rx] The first IBM PC virus in the “wild” was a boot sector virus dubbed (c)Brain,[rx] created in 1986 by Amjad Farooq Alvi and Basit Farooq Alvi in Lahore, Pakistan, reportedly to deter unauthorized copying of the software they had written.[rx] The first virus to specifically target Microsoft Windows, WinVir was discovered in April 1992, two years after the release of Windows 3.0.[rx] The virus did not contain any Windows API calls, instead of relying on DOS interrupts. A few years later, in February 1996, Australian hackers from the virus-writing crew VLAD created the Bizatch virus (also known as the “Boza” virus), which was the first known virus to target Windows 95. In late 1997 the encrypted, memory-resident stealth virus Win32. Cabanas was released—the first known virus that targeted Windows NT (it was also able to infect Windows 3.0 and Windows 9x hosts).[rx]
Even home computers were affected by viruses. The first one to appear on the Commodore Amiga was a boot sector virus called the SCA virus, which was detected in November 1987.[rx]
FAQ
What is the 5 computer virus?
- Conficker, Downup, Downadup, Kido – these are all computer virus names that appeared on the internet in 2008. It used the MS08-067 Windows system vulnerability and advanced malware techniques to propagate and install itself into the system.
What are the 10 computer viruses?
Dr. Md. Harun Ar Rashid, MPH, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including MPH, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and research, writing and inventory creative thinking, innovative idea, critical care managementing make in his community to outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices.
