Malware: What Is It and How to Protect Against It?

Janis von Bleichert
Last update
8. Sep 2023

Online danger has many names, but one of the most common is malware. Otherwise known as malicious software, this includes viruses, Trojans, ransomware, spyware, and adware: Basically, any type of program that attempts to manipulate or damage your files, money, and privacy. The constant struggle between malware and anti-malware dominates the world of cybersecurity.

Nearly 3,000 years ago, the Chinese philosopher Sun Tzu famously concluded that knowing your enemy (and yourself) is the key to winning any battle. In this article, we're going to introduce you to malware, show what kinds exist, what sort of damage they can do, and how to best protect yourself against them.

What Types of Malware Are There?

Cybercriminals don't wear elaborate costumes, but they're just as creative as The Joker or any other supervillain: New malware variants appear on a daily, if not hourly basis. With that said, there are several different kind of malware:

  • Computer virus
    These programs or program codes are concealed in 'hosts' like program installation files. When a file containing a virus is opened, the latter launches its attack against the system. Often, it rapidly multiplies and tries to overwhelm the user's attempts to delete it or close its processes. In nearly every case, viruses are negative and will delete files, limit functionality, and even sabotage an infected system's hardware.

  • Trojans
    At the moment, these are the most common type of malware. Trojans disguise themselves as legitimate programs but perform harmful actions on your system without your knowledge. The damage is wide-reaching: Trojans can delete, modify, or block access to files, import illegal files onto your system, or monitor your passwords and other sensitive information.

  • Ransomware
    Ransomware, or "extortion Trojans" digitally take your files hostage, only releasing them in exchange for a ransom. In practice, your system or folders are remotely locked (encrypted), and you need to pay the ransomer large sums of money for the decryption key. Infamous examples include Locky and WannaCry, both of which caused around $4 billion USD of damages worldwide.

  • Spyware
    Although less ruthless than ransomware, spyware observes and monitors your activity, rather than compromising itself and attacking you outright. Like any good secret agent, these sneak into your system, collect information about your activity without your knowledge, and transmit it to third parties, like advertisers.

  • Adware
    This is like spyware's loudmouth little brother. Adware disguises itself as a legitimate program to flood your computer with shady ads. You'll know you have an adware infection because multiple pop-ups, perhaps for pornographic websites, will suddenly appear on your desktop. Like spyware, adware can also damage your privacy by relaying your data and activity to third parties.

  • Botnet
    Botnets are networks of compromised systems that your computer is part of without your knowledge. Like a parasite, cybercriminals use these to smuggle bots onto your system and utilize your resources. In this way, third parties don't just gain access to sensitive files but also use your computer for illegal activities.

  • Crypto Miner
    Illegal crypto-mining harnesses the resources of other systems to maximize cryptocurrency mining.

  • Phishing
    For this, cybercriminals send counterfeit emails to access sensitive data, like passwords or account credentials.

What Kind of Damage Can Malware Cause?

Even though malware pursues illegal or negative outcomes and activities, these vary from type to type. Some effects are immediately noticeable, whereas others remain hidden until the program is detected. These range in scope from annoying (countless pop-ups appearing on your desktop) to financially disastrous. How much damage is caused depends on the infected device and the amount of sensitive data it contains.

In general, malware can cause the following problems:

  • Encrypt or delete files
    Ransomware is notorious for encrypting files without the user's knowledge. Access to important data is lost, and can only be returned by paying a sizable ransom. Many other kinds of malware can and do delete, steal, or otherwise misuse files on your system.

  • Collect bank data and passwords
    Spyware, phishing, and other types of malware secretly attempt to gain access to your most sensitive data. Common targets include passwords, which give hackers the digital keys to your accounts, as well as banking information, and credit card numbers.

  • Limit performance
    Often, the first symptom of a malware infection is a drop in your system's performance. Should your computer suddenly be much slower than usual, chances are that a program is misusing your system's resources for its own purposes, such as illegal crypto mining.

Even for individual users, malware can cause considerable damage, both financially and in terms of privacy. However, the risks are even greater for companies and organizations: Financial damage resulting from successful malware attacks can quickly cost millions, with losses in data or intellectual property plunging companies into ruin. The clock starts ticking the moment malware burrows into your system.

How Do I Know if My Device Is Infected?

It can be difficult to determine if your system has been infected without specialized software. With the exception of multiple pop-up ads or a ransomware notice, most malware tries to stay hidden for as long as possible. This way, they can maximize the theft of your data and/or resources. There are, however, some symptoms of a malware infection:

  • Your device is slower than usual
    When your system's performance suddenly drops, there's a good chance that its resources have been co-opted by malware.
  • Pop-ups and unauthorized programs appear
    Do pop-ups or tabs to shady websites automatically open? If so, your system probably has a malware infection.

How Can I Protect Myself Against Malware?

If you suspect infection

Has malware already infected your system, or do you have a feeling that it has? Don't waste any time. Luckily, there are many programs dedicated to finding, identifying, and neutralizing malware. Be sure to check out our step-by-step malware removal guide.

The best protection: Prevention

You can be even safer by not letting malware become an issue in the first place. To do this, brush up on good browsing and surfing behavior and use dedicated software. Some of the former include:

  • Regular system and software updates
    Malware thrives on finding new exploits or weaknesses in programs since these allow it to infiltrate systems. For this reason, keep your installed programs and your system (especially if it's Windows) updated. Most programs and operating systems automatically find updates but will require your permission to install them - Don't procrastinate.

  • Install anti-malware software with real-time protection
    Anti-malware software is great at preventing and neutralizing malware infections. Real-time protection stops harmful programs from getting comfy on your system. With these, you can scan your system for threats and remove any that are found.

    Since there are so many anti-malware programs, you're probably wondering what the best is. To find out, look no further than our comprehensive and exhaustive evaluation of the top 15 providers.


The best defenses against malware are common sense, vigilance, responsible Internet and computer behavior, and anti-malware software. Just err on the side of caution, don't open strange links or emails from unknown senders, and regularly update and run a reliable anti-malware program to stay safe online.

Janis von Bleichert studied business informatics at the TU Munich and computer science at the TU Berlin, Germany. He has been self-employed since 2006 and is the founder of He writes about hosting, software and IT security.
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