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What is a computer virus?A computer virus is a type of malware that attaches itself to other programs, self-replicates, and spreads from one computer to another. When a virus infects a computer, it makes copies of itself and attaches to other files or documents. It then modifies those files and continues to spread. Viruses infect computers discreetly, and they’re often designed to destroy personal files or gain control of devices. Making copies of themselves, computer viruses spread across devices and networks like biological viruses passing from one person to the next. And just like the biological versions, some computer viruses are simply annoying while others can cause major damage. A computer virus is a type of malicious software that attaches itself to other programs, self-replicates, and spreads to other computers. So, what’s the difference between a virus and malware (malicious software)? Virus is often a catch-all term used to refer to any kind of software created to be harmful. But a virus is just one type of malware, and the definition of a virus is that it’s a computer program that can self-replicate, infect other programs, and spread to other computers. How do computer viruses work?Computer virus is an umbrella term that includes many different types of viruses, delivery mechanisms, and impacts. To understand how computer viruses work, it’s helpful to split them into two categories: those that begin to infect and replicate as soon as they land on your computer, and those that lie dormant, waiting for you to unwittingly execute the code. A computer virus can begin infecting your computer immediately, or it can wait for you to unwittingly trigger it.Computer viruses have four phases (inspired by biologists’ classification of a real-life virus’s life cycle).
How do computer viruses spread?Typically, computer viruses spread through malicious online downloads, infected email attachments, or by plugging in infected hardware like an external flash drive (USB stick). Computer viruses can spread through almost any method of file sharing, as long as the virus can avoid detection by antivirus programs. Here are some common ways computer viruses spread and can end up on your computer:
Good computer hygiene and anti-malware tools can guard you against all of these attack vectors. So it’s important to keep your software updated, use strong passwords, and shield your device with strong cybersecurity software. What computer viruses doComputer viruses hijack your system’s code and resources in order to replicate, causing performance issues on all device types. When executed, a computer virus releases its payload and begins its attack. Almost immediately, you’ll start to see the impact of what computer viruses can do. What can viruses do to your computer? Here are some of the effects they can unleash:
Aside from causing these negative performance issues, computer viruses can also steal personal data — such as usernames, passwords, and credit card details. Some viruses can spam all of your contacts and try to trick them into downloading the virus as well, which is another way they spread. Can all devices get viruses?All devices, including Macs, can get viruses. iPhones and Androids can get viruses too. In fact, any device with internet access can get malware — even smart devices like coffee makers. But it’s worth remembering the distinction between malware and viruses: a virus is just one type of malware. And there are many types of infections that can damage your device, steal your data, and otherwise wreak havoc. From ransomware to spyware to trojans, there are some nasty strains of malware to watch out for on all your gadgets. Thankfully, many of these threats can be wiped out and prevented with trusted free antivirus software. Different types of computer virusesEven if we're talking strictly about viruses (as opposed to other forms of malware), there are still many different types of computer viruses. Here are a few different types of computer viruses that have been found spreading through the internet: Direct action virusThe most common type of virus and the easiest to create, direct action viruses enter your computer, cause chaos (usually by attaching themselves to a lot of COM or EXE files), then delete themselves. The famous Vienna virus searched for COM files to infect and/or destroy, and while it was the first virus ever defeated by an antivirus program in 1987, the fix wasn’t available to those living under communist regimes. In 1988, Avast co-founder Pavel Baudis also beat the virus and brought the solution to those who couldn’t access the first fix. Boot sector virusAs the name suggests, boot sector viruses sneak into your boot sector (responsible for loading your computer’s operating system upon startup) to infect your memory right away. These types of viruses traditionally spread through hardware, such as floppy disks, USB drives, and CDs. As those devices become obsolete, this type of virus is also on its way out. One leftover variety that emerged in 2014 is called the Stoner virus, because it displayed on-screen messages in support of marijuana legalization. Resident virusA resident virus is another type of memory-infecting virus that sets up shop in your RAM (random access memory), which lets the virus persist even if you remove the original infector. A notable example was the Magistr virus, which spreads to your friends by spamming your contact list. It also deletes files and destroys computer motherboard’s memory. Multipartite virusIncreasing their power by infecting both your files and your boot space, multipartite viruses are brutal. They’re very hard to eradicate because they can hide themselves in either files or the boot space. The Invader virus was one such example, which began overwriting your hard drive as soon as you hit CTRL + ALT + DEL to try to get rid of it. Polymorphic virusAnother stubborn type of virus, polymorphic viruses hide by changing shape. As they replicate, their clones are all slightly different, which helps avoid detection. One example is the VirLock virus, which changes shape while also incorporating a bit of ransomware that locks up your files until you pay to release them. Macro virusMacro viruses are created to hide inside word document files, such as DOC or DOCX files. When you download the file, you’ll be prompted to enable macros — as soon as you do, you trigger the computer virus. Infected macros have also been used in ransomware, such as the Locky strain, which targeted healthcare institutions, encrypting their files and demanding payment to decrypt them. Avoiding the latest computer virus threatsAs with any type of malware, prevention is the best medicine. Good digital hygiene and sensible browsing habits can help you avoid the latest computer virus threats. Here are some other tips to keep in mind:
Signs your computer is infected with a virusOne obvious sign your computer is infected with a virus is if your friends start receiving suspicious messages sent from your email account. A classic way viruses spread is by spamming the contact list of an infected device — using email, text, or another messaging service — and trying to trick recipients into downloading the malware. There are several other symptoms of a computer virus to look out for, including:
A free malware removal tool will monitor your device in real time to detect, block, and remove viruses and other malware. Remove a computer virusIf you think you already have a virus or other malware on your system, perform a quick scan and remove it with our award-winning free virus removal tool. Our virus scans will make sure your computer remains free from viruses and other malware. For detailed steps on getting rid of viruses and other malicious code on your computer or mobile phone, check out our dedicated virus removal guides:
Get ironclad protection against computer virusesNow that you know what a computer virus is, the importance of preventing viruses from infecting your device should come as no surprise. Avast’s advanced threat-detection network blocks tens of millions of threats daily, automatically detecting viruses and malware and stopping them from ever reaching your computer. Along with prevention, Avast One will help you find and remove any viruses or other malware already on your system. Plus, you’ll get extra protection against malicious links and downloads, unsafe websites, and threats to your network. Download Avast One and never worry about getting infected with a computer virus again. Which of the following types of malware is a piece of code or software that spreads from system to system?One of the most common types of malware, worms spread over computer networks by exploiting operating system vulnerabilities. A worm is a standalone program that replicates itself to infect other computers, without requiring action from anyone.
Which of the following is a piece of code or software designed to lie in wait on a system until a specified event occurs?A logic bomb is a malicious piece of code that's secretly inserted into a computer network, operating system, or software application. It lies dormant until a specific condition occurs.
Which of the following is a self replicating piece of software?A Worm is a self-replicating program. It is self-contained and does not require a host program. The program creates the copy and causes it to execute; no user intervention is required. Worms commonly utilize network services to propagate to other computer systems [19].
Which of the following types of viruses possesses code allowing it to hide and mutate itself in random ways that prevent detection?A polymorphic virus includes an encrypted payload and a mutation engine. The encryption hides the malicious payload from scanners and threat detection software, which are left to identify the virus by its decryption routine.
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