Your usual homepage may change to another website, for instance. Plus, you may be unable to reset it. Mass emails being sent from your email account. A criminal may take control of your account or send emails in your name from another infected computer.
Frequent crashes. A virus can inflict major damage on your hard drive. This may cause your device to freeze or crash. It may also prevent your device from coming back on. Unusually slow computer performance. A sudden change of processing speed could signal that your computer has a virus.
Unknown programs that start up when you turn on your computer. You may become aware of the unfamiliar program when you start your computer.
Unusual activities like password changes. This could prevent you from logging into your computer. How to help protect against computer viruses? How can you help protect your devices against computer viruses? Here are some of the things you can do to help keep your computer safe. What are the different types of computer viruses? Boot sector virus This type of virus can take control when you start — or boot — your computer. Web scripting virus This type of virus exploits the code of web browsers and web pages.
Direct action virus This type of virus comes into action when you execute a file containing a virus. Polymorphic virus A polymorphic virus changes its code each time an infected file is executed.
File infector virus This common virus inserts malicious code into executable files — files used to perform certain functions or operations on a system. Multipartite virus This kind of virus infects and spreads in multiple ways.
Macro virus Macro viruses are written in the same macro language used for software applications. How to remove computer viruses You can take two approaches to removing a computer virus.
Separately, Norton also offers a free, three-step virus clean-up plan. Run a free Norton Security Scan to check for viruses and malware on your devices. Note: It does not run on Mac OS.
Need help? A Norton tech can assist by remotely accessing your computer to track down and eliminate most viruses. Install up-to-date security software to help prevent future malware and virus threats. Editorial note: Our articles provide educational information for you. NortonLifeLock offerings may not cover or protect against every type of crime, fraud, or threat we write about.
Our goal is to increase awareness about cyber safety. Please review complete Terms during enrollment or setup. At this point, the virus propagates itself by infecting other applications on the host computer, inserting its malicious code wherever it can. A resident virus does this to programs as they open, whereas a non-resident virus can infect executable files even if they aren't running. Boot sector viruses use a particularly pernicious technique at this stage: they place their code in the boot sector of the computer's system disk, ensuring that it will be executed even before the operating system fully loads, making it impossible to run the computer in a "clean" way.
Once the virus has its hooks into your computer, it can start executing its payload, which is the term for the part of the virus code that does the dirty work its creators built it for. These can include all sorts of nasty things: Viruses can scan your computer hard drive for banking credentials, log your keystrokes to steal passwords, turn your computer into a zombie that launches a DDoS attack against the hacker's enemies, or even encrypt your data and demand a bitcoin ransom to restore access.
Other types of malware can have similar payloads, of course: there are ransomware worms and DDoS Trojans and so forth. In the early, pre-internet days, viruses often spread from computer to computer via infected floppy disks. The SCA virus, for instance, spread amongst Amiga users on disks with pirated software. Today, viruses spread via the internet. In most cases, applications that have been infected by virus code are transferred from computer to computer just like any other application.
Because many viruses include a logic bomb — code that ensures that the virus's payload only executes at a specific time or under certain conditions — users or admins may be unaware that their applications are infected and will transfer or install them with impunity. Infected applications might be emailed inadvertently or deliberately — some viruses actually hijack a computer's mail software to email out copies of themselves ; they could also be downloaded from an infected code repository or compromised app store.
One thing you'll notice that all of these infection vectors have in common is that they require the victim to execute the infected application or code. Remember, a virus can only execute and reproduce if its host application is running! Still, with email such a common malware dispersal method, a question that causes many people anxiety is: Can I get a virus from opening an email? The answer is that you almost certainly can't simply by opening a message; you have to download and execute an attachment that's been infected with virus code.
That's why most security pros are so insistent that you be very careful about executing email attachments, and why most email clients and webmail services include virus scanning features by default.
A particularly sneaky way that a virus can infect a computer is if the infected code runs as JavaScript inside a web browser and manages to exploit security holes to infect programs installed locally. Some email clients will execute HTML and JavaScript code embedded in email messages, so strictly speaking, opening such messages could infect your computer with a virus.
But most email clients and webmail services have built-in security features that would prevent this from happening, so this isn't an infection vector that should be one of your primary fears.
Symantec has a good breakdown on the various types of viruses you might encounter , categorized in different ways. We've already met resident and non-resident viruses , boot sector viruses , web scripting viruses , and so on. There are a couple other types you might want to be aware of:. Keep in mind that these category schemes are based on different aspects of a virus's behavior, and so a virus can fall into more than one category.
A resident virus could also be polymorphic, for instance. Antivirus software is the most widely known product in the category of malware protection products. CSO has compiled a list of the top antivirus software for Windows , Android , Linux and macOS , though keep in mind that antivirus isn't a be-all end-all solution.
But what you do proactively can reduce your chances of getting a virus in the first place. While there are solutions for ridding your computer of malicious viruses, it can be a time-consuming and expensive headache to fix. Home Blog What is a Computer Virus? And How to Avoid Infection in What is a Computer Virus?
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