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

Janis von Bleichert
Last update
16. Mar 2023

Danger on the Internet has a name: Malware. The portmanteau of "malicious software", which includes viruses, Trojans, ransomware, spyware, and adware, denotes any type of program that attempts to subvert or even manipulate your files, money, and privacy. The world of Internet security can largely be seen as a constant tug-of-war between malware and anti-malware.

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

What Types of Malware Are There?

Cybercriminals don't have elaborate costumes, but they are just as creative as The Joker or any other supervillain, as can be seen in the emergence of new malware variants on a daily, if not hourly basis. With that said, these types of software can be grouped into several general categories:

  • Computer virus
    Computer viruses are programs or program codes concealed in 'hosts' such as executable files (program installation data). When a user opens a file that contains a virus, the latter will run, attacking the system and often, multiplying itself, overwhelming any attempts by the user to delete the file or its processes. In nearly every case, a virus will have an adverse impact on a system, deleting files, limiting system usage or functionality, or even attacking its hardware.

  • Trojans
    As of the time of writing, Trojans are the most prevalent form of malware on the Internet. These disguise themselves as legitimate programs but perform undesired and harmful actions on your system without your knowledge. This damage is wide-ranging: Trojans can delete, modify, or remove access to files, import illegal files onto your system, or monitor your passwords and other sensitive information.

  • Ransomware
    Ransomware are also known as "extortion Trojans" since they take your files (digitally) hostage, only freeing them in exchange for a ransom. In practice, this unfolds as a remote locking of your system, and the encryption of certain files for large sums of money. Infamous examples of this type of malware include Locky and WannaCry, both of which caused around $4 billion USD of damages worldwide.

  • Spyware
    Spyware is less ruthless than ransomware, primarily because it is more interested in remaining undetected and observing your activity, rather than compromising itself and attacking you outright. Like any good secret agent, these clandestinely find their way into your system, collecting information about your activity without your approval, and transmitting it to third parties, such as advertisers.

  • Adware
    Adware can be seen as complementary to spyware, but unlike its distant relative, does not have secrecy in mind. Adware is software that disguises itself as a legitimate program in order to flood your computer with advertisements for dubious products or services. This can be readily noticed when, for example, multiple pop-ups for pornographic websites open on your desktop. Similarly to spyware, adware can also relay your data and activity history to third parties, negatively impacting your privacy.

  • Botnet
    Botnets are networks of compromised systems, to which your computer, unbeknownst to you, is attached. These allow cyber criminals to smuggle so-called bots onto your system and utilize your resources. In this manner, third parties can not only gain access to sensitive files but also use your computer for illegal purposes without your knowledge.

  • Crypto-Miner
    Illegal crypto-mining utilizes the resources of other systems to maximize the mining of cryptocurrencies, such as Bitcoin.

  • Phishing
    Phishing refers to counterfeit emails that are sent by cybercriminals to gain access to sensitive data, such as passwords or account information.

What Kind of Damage Can Malware Cause?

As its name suggests, malware pursues bad or adverse ends. What exactly these do varies from program to program. Some effects can be noticed immediately, whereas others remain unknown until the program is detected. Similarly, some of these are simply annoying (such as the opening of countless pop-up ads on your desktop) whereas others can cost you or your business a significant sum of money. The amount of damage varies widely according to the type of device, and the amount of sensitive data it contains.

In general, however, malware can cause the following problems:

  • Encrypt or delete files
    Ransomware in particular is known for encrypting your files without your knowledge. This results in a loss of access to important data, which can only be reversed 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 surreptitiously attempt to gain access to your most sensitive data. These include passwords, with which hackers can gain access to your accounts, as well as banking information and credit card numbers.

  • Limit performance
    The first symptom of a malware infection is often a drop in your system's performance. Should your computer suddenly be much slower than usual, it is more than likely 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.

For that reason: The clock starts ticking the moment malware burrows into your system.

How Do I Know if My Device Is Infected?

Depending on the type of malware that has infected your system, it can be difficult to determine if your system has been infected without having special software to do this. With the exception of the multiple pop-up ads associated with adware, most types of malware rely on remaining unnoticed for as long as possible, since, in this manner, 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 suddenly experiences a drop in performance, it is possible that its resources have been co-opted by malware.
  • Pop-ups and unauthorized programs appear
    Do pop-ups or tabs open automatically to questionable websites? If so, your system is most likely infected with malware.

How Can I Protect Myself Against Malware?

If you suspect infection

Has malware already infected your system, or do you strongly believe this to be the case? Don't waste any time. Luckily, there are many programs that are dedicated to finding, identifying, and neutralizing malware. Here, we'll show you how to remove malware step-by-step.

The best protection: Prevention

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

  • Regular updates (system & programs)
    Malware thrives on finding new exploits or weaknesses in programs, through which it can operate without the system or user being any the wiser. For that reason, it is critical to keep any programs that you have installed, as well as 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 dally on approving them.

  • Install anti-malware software with real-time protection
    Anti-malware software excels in both preventing and besting malware. Real-time protection ensures that damaging programs are stopped before they can make themselves comfortable on your system, acting as a sort of virtual bouncer. These programs also allow you to scan your system for threats, removing them if found.

    Since the number of anti-malware programs is fairly large, 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 defense against malware is a combination of vigilant and sensible behavior on the Internet, proper computer usage, and anti-malware software. By erring on the side of caution when surfing the web, not opening strange links or emails from unknown senders, and regularly updating and running an anti-malware program, you'll be relatively safe from the manifold dangers of the Internet.

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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