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The Ultimate Guide to Malware

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We’ve all had run-ins with malicious software, which is exactly what malware means — any software designed to cause harm.

Malware can damage files, steal sensitive data, and even take your device hostage. Find out what malware is, how it works, what it can do, and how you can protect yourself against it with reliable antivirus software.

What is malware?

Malware is any type of software created to harm or exploit another piece of software or hardware. Short for “malicious software,” malware is a collective term used to describe viruses, ransomware, spyware, Trojans, and any other type of code or software built with malicious intent.

It’s this malicious intent that characterizes the malware definition — the meaning of malware is the damage it can inflict on a computer, computer system, server, or network. It’s the how and the why that separate one type of malware from the next.

Is malware a virus?

All viruses are malware, but not all types of malware are viruses. Viruses are a type of malware that self-replicate by inserting their code into other files or programs, then spreading from one infected device to another.

To know whether an infection is caused by another type of malware or a virus, you need to look at how it works. If it isn’t using other programs to copy itself and spread, then it’s not a virus.

What can malware do, and how dangerous is it?

Malware attacks can crack weak passwords, bore deep into systems, spread through networks, and disrupt the daily operations of an organization or business. Other types of malware can lock up important files, spam you with ads, slow down your computer, or redirect you to malicious websites.

Malicious software is at the root of most cyberattacks, including the large-scale data breaches that lead to widespread identity theft and fraud. Malware is also behind the ransomware attacks that result in millions of dollars in damages. Hackers aim malware attacks against individuals, companies, and even governments.

What are the signs of a malware infection?

The world of malware is diverse, but many types of malware share similar warning signs. Monitor your device for the following symptoms of a malware infection:

  • Sudden performance drops: Malware can occupy a lot of your device’s processing power, resulting in severe slowdowns. That’s why removing malware is one way to speed up your PC.
  • Frequent crashes and freezing: Some malware will cause your computer to freeze or crash, while other types will cause crashes by consuming too much RAM or driving up CPU temperatures. Sustained high CPU usage may be a sign of malware.
  • Deleted or corrupted files: Malware often deletes or corrupts files as part of its plan to cause as much chaos as possible.
  • Lots of pop-up ads: Adware’s job is to spam you with pop-ups. Other types of malware may cause pop-up ads and alerts as well.
  • Browser redirects: If your browser keeps sending you to sites that you aren’t trying to visit, a malware attack may have made changes to your DNS settings.
  • Your contacts are receiving strange messages from you: Some malware spreads by emailing or messaging victims’ contacts. Secure messaging apps can help protect your communications from eavesdroppers.
  • You see a ransom note: Ransomware wants you to know it’s there — it’ll take over your screen with a ransom note demanding payment to get your files back. A ransom note is an easy way to tell what malware is on your computer: it’s ransomware.
  • Unfamiliar apps: Malware can install additional apps on your device. If you see new programs that you didn’t install yourself, it may be the result of a malware attack.

Certain strains of malware are easier to detect than others. Ransomware and adware are usually visible immediately, while spyware wants to stay hidden. The only surefire way to detect all malware before it infects your PC, Mac, or mobile device is with a dedicated antivirus tool.

AVG AntiVirus FREE combines one of the world’s largest threat-detection networks with an award-winning cybersecurity engine to scan and remove malware on your device, while blocking any new malware trying to infect it.

Why do hackers and cybercriminals use malware?

  • Data theft: Dangerous cybercriminals can steal data and use it to commit identity theft or sell it on the dark web to other cybercriminals. Malware-based data theft can involve redirecting people to pharming websites, capturing passwords with spyware, and even large-scale data breaches.
  • Corporate espionage: Data theft on a corporate scale is known as corporate espionage. Companies can steal secrets from their competitors, and governments often target large corporations as well.
  • Cyberwarfare and international espionage: Governments around the world are frequently accused of using malware against other countries and large corporations.
  • Sabotage: Sometimes, damage is the goal. Attackers can delete files, wipe records, or shut down entire organizations to cause millions of dollars of damage.
  • Extortion: Ransomware encrypts a victim’s files or device and demands payment for the decryption key. The purpose is to get the victim — a person, institution, or government — to pay the ransom.
  • Law enforcement: Police and other government authorities can use spyware to monitor suspects and harvest information to use in their investigations.
  • Entrepreneurship: Many potent strains of ransomware are available to anyone as ransomware-as-a-service (RaaS), where the developer licenses their malware in exchange for an up-front fee or a cut of every payment.
  • DDoS attacks: Hackers can use malicious software to create botnets — linked networks of “zombie computers” under the attacker’s control. The botnet is then used to overload a server in a distributed denial of service (DDoS) attack.
  • Mining cryptocurrency: Cryptominers force a victim’s computer to generate, or mine, bitcoin or other cryptocurrency for the attacker.

Types of malware

Common types of malware include viruses, Trojans, spyware, keyloggers, worms, ransomware, adware, scareware, rootkits, cryptominers, and logic bombs. The categories are based on how malware works and how it spreads.

  • Viruses: Computer viruses infect clean files and spread to other clean files. They can spread uncontrollably, damaging a system’s core functionality and deleting or corrupting files. The history of viruses reaches back to the 1980s.
  • Macro viruses: Macro viruses are a type of virus that exploit macros in Microsoft Office apps like Word and Excel to infect your device.
  • Router viruses: Your Wi-Fi router can also become infected with malware. Router malware usually redirects you to malicious pharming websites that can capture your personal data, and removing router viruses can be tricky.
  • Trojans: Trojans are disguised as legitimate software or are hidden in legitimate software that’s been tampered with. A Trojan’s job is to sneak onto your device and install additional malware.
  • Spyware: Spyware is malware designed to spy on you. It hides in the background and collects your data, including passwords, GPS location, and financial information. Fortunately, removing spyware from your Mac or PC usually isn’t very difficult.
  • Keyloggers: Keyloggers are a type of spyware that hide on your device while recording all your keystrokes. They can capture login credentials, credit card numbers, and more.
  • Worms: Worms are a bit different from viruses, because they can spread without a host file. Worms infect entire networks of devices, using each consecutively infected machine to infect others.
  • Ransomware: Ransomware locks up your computer and your files, and threatens to erase everything unless you pay a ransom. It’s one of today’s most pressing malware threats.
  • Adware: Adware is malicious software that spams you with ads to generate revenue for the attacker. Adware undermines your security to serve you ads — which can give other malware an easy way in.
  • Scareware: Scareware uses social engineering tricks to frighten you into installing it. A fake pop-up warns you that your computer is infected with a virus, and the solution will be to download a scam “security” program.
  • Botnets: Botnets aren’t technically malware — they’re networks of infected computers that work together under the control of an attacker. Botnets are often used to commit DDoS attacks.
  • Rootkits: Rootkits are a dangerous, hard-to-detect form of malware that burrow deep into your computer to give a hacker full administrative access. The best way to deal with them is by using a dedicated rootkit removal tool.
  • rowser hijackers: Browser hijackers are malware that modify your web browser without your consent, and often without your knowledge. They may redirect you to harmful websites or spam you with extra ads. Removing browser hijackers usually is quite simple, but it’s always good to use secure and private browsers.
  • Cryptominers: Cryptominer malware is malicious software that hijacks a victim’s computer’s processing power to mine cryptocurrency for the attacker in a practice known as cryptojacking. Many cryptominers use browser hijacking to take over computers.
  • Logic bombs: Logic bombs are bits of malicious code designed to execute after a specified condition has been met. Time bombs are a subset of logic bombs that lie dormant until a certain time or date.

How does malware work?

For malware to work, it usually needs you to do something first to get the software on your computer. That means clicking a link, opening an attachment, or visiting an infected website. Once on your machine, the malware’s payload begins the task it’s designed to perform — stealing your data, encrypting your files, installing additional malware, and so on.

Malware will stay on your system until it’s been detected and removed. And some malicious software will try to block or hide from any antivirus apps or other security tools you may have.

How does malware spread?

Malware can spread in a variety of ways: when you download and install an infected program, when you click an infected link or open a malicious email attachment, or even if you use corrupted physical media like an infected USB drive.

Types of malware attacks

Here are some of the most common malware attack types to watch out for.

  • Email: If your email has been hacked, malware can force your computer to send emails with infected attachments or links to malicious websites. When a recipient opens the attachment or clicks the link, the malware is installed on their computer, and the cycle repeats. Not opening attachments from unknown senders is an important part of good email security.
  • Messaging apps: Malware can spread by hijacking messaging apps to send infected attachments or malicious links to a victim’s contacts.
  • Infected ads: Hackers can load malware into ads and seed those ads on popular websites — a practice known as malvertising. When you click the infected ad, it downloads malware to your computer.
  • Pop-up alerts: Scareware uses fake security alerts to trick you into downloading bogus security software, which in some cases can be additional malware.
  • Drive-by downloads: A drive-by download happens when a malicious website automatically downloads malware onto your device. This happens as soon as you load the page — no clicks required. Hackers use DNS hijacking to automatically redirect you to these malicious sites.
  • Personal installation: People sometimes install parental control software on their partner’s computer or phone. When these apps are used without the victim’s consent, they become spyware.
  • Physical media: Hackers can load malware onto USB flash drives and wait for unsuspecting victims to plug them into their computers. This technique is often used in corporate espionage.
  • Exploits: Exploits are bits of code designed to take advantage of a vulnerability, or security weakness, in a piece of software or hardware. A blended threat is a specialized type of exploit package that targets multiple vulnerabilities at once.

Malware can infect your computer through a variety of vectors, including email, ads, pop-up alerts, and more.Malware can spread in a variety of ways.

Real-life malware attacks

Many malware attacks happen silently, with victims never realizing the attack happened. Some malware attacks are so dangerous and widespread, they send shockwaves around the world. Here are some of the most notorious malware examples:

  • Vienna virus: The history of malware began in the 1960s with relatively harmless viruses that spread without causing much damage. It wasn’t until the late 1980s that malware turned nasty with the Vienna virus. The Vienna virus corrupted data and destroyed files — and led to the creation of the world’s first antivirus tool.
  • WannaCry: In 2017, WannaCry quickly became the largest ransomware attack in history. It paralyzed governments, hospitals, and universities around the world and caused roughly $4 billion in damage.
  • Petya and NotPetya: These two ransomware strains both arrived in 2017, spreading far and wide — including to Ukraine’s national bank. The Petya and NotPetya malware attacks resulted in around $10 billion in damages worldwide.
  • Equifax data breach: Hackers pulled off one of the most devastating data breaches in history when they managed to crack US credit bureau Equifax in 2017, accessing the sensitive personal data of 147 million people.

COVID-19 phishing scams

In 2020, many cybercriminals took advantage of COVID-19 fears in a series of phishing and malware attacks. From spoofing the World Health Organization to offering fake remote jobs, hackers used phishing attacks to deploy malware and hijack sensitive personal data.

How to detect, remove, and prevent malware

When it comes to malware, prevention is better than a cure. Incorporate the following tips into your digital lifestyle to minimize your malware risk and protect yourself against a potential attack.

Don’t trust strangers online. Strange emails, abrupt alerts, fake profiles, and other scams are the most common methods of delivering malware. If you don’t know exactly what something is, don’t click on it.

Double-check your downloads. From pirating sites to official storefronts, malware is often lurking just around the corner. Before downloading, always double-check that the provider is trustworthy.

Get an ad blocker. Malvertising — where hackers inject malicious code into otherwise legitimate advertising networks — is on the rise. Counter it by blocking ads with a reliable ad blocker. Some infected ads can download malware as soon as they load on your screen, without needing you to even click on them.

AVG Secure Browser is a free browser that includes an array of built-in features, including an ad blocker, to protect your privacy and secure your device against malware.

Be careful where you browse. Malware can be found anywhere, but it’s most commonly found on websites with poor backend security. If you’re visiting a large, reputable site, your risk of encountering malware is minimal.

Always update your software. Outdated software may have security vulnerabilities, which developers routinely patch with software updates. Always install updates for your operating system (OS) and other software as soon as they become available.

Protect your devices with an antivirus app. Even if you follow all of the advice above, your device might still get infected with malware. For optimal protection, combine smart online habits with powerful anti-malware software like AVG AntiVirus FREE, which detects and stops malware before it can infect your PC, Mac, or mobile device.

Download AVG AntiVirus FREE

Can Macs and phones be affected by malware?

PCs aren’t the only devices that get malware — phones and Macs can get malware, too. Any device connected to the internet is at risk, including your Mac, mobile phone, or tablet.

While Apple is quick to patch macOS against zero-day attacks, Macs have faced an increasing number of malware threats in recent years. A Mac malware removal tool can help keep your Mac free of infections.

Meanwhile, Android and iOS malware continues to emerge. From Android spyware to Android ransomware, there are plenty of threats to your device. And while there aren’t any iPhone viruses, iOS isn’t entirely threat-proof — especially if you’ve jailbroken your phone. But even sneaky malware like spyware can be removed from your iPhone with the right steps and tools:

What to do if your device is infected by malware?

An antivirus scan is the best way to detect and remove malware from your computer or clear a malware infection on your phone. Use a reliable malware removal tool to scan your device, find the malware on it, and clear the infection. Then, restart your device and scan it again to make sure the infection has been completely removed.

An anti-malware security app will scan your device for malware and other threats.

Before clearing the malware, you may need to restart your device in Safe Mode first to prevent the malicious software from affecting your antivirus tool.

Protect yourself against malware with a world-class antivirus solution

With so many types of malware out there, it’s hard to avoid them all. In addition to following all the malware prevention guidance above, you should partner with a world leader in cybersecurity. AVG AntiVirus FREE is an award-winning anti-malware tool that defends your devices against malware in real time.

Detect and block all types of malware before they infect your devices, and clear up any infections you may currently have. Plus, get always-on protection against Wi-Fi vulnerabilities and phishing attacks. Start protecting your devices and your data today with AVG.

Image credit: Sora Shimazaki

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  1. Glary Software is a good free cleaner
    Ultra Virus Killer SOS picks up DNS trackers where others won’t with SFC Scan
    And of course Malware Bytes Adware cleaner
    All free


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