What is malware?
Malware is malicious software designed to damage or break into computer systems. There are many malware categories, each with its own spin on how it sneaks onto devices or into networks. Some strains hide quietly for weeks before launching an attack, while others make a big splash right away.
Either way, knowing the characteristics of malware is the first step in defending your business against these stealthy threats. Here are the 10 types of malware that pose the biggest threat to businesses:
Ransomware
Still leading the pack among the many types of malware out there, ransomware locks your files and demands that you pay up to get them back. The attacker might even threaten to leak stolen data if you refuse. Imagine your finance team waking up to find the entire accounting system encrypted—that’s how quickly ransomware can halt your operations.
Trojans
A trojan looks innocent—like a legitimate software download or email attachment—but once you run it, it opens the backdoor for attackers to waltz right in. It might pose as a helpful system tool, a cute game, or maybe even a security update. The unsuspecting user believes they’re installing something useful and never realizes that they’ve literally invited the enemy inside.
Worms
Unlike trojans, worms can spread across systems without any help from your employees. You might have one infected machine on your network, and before you know it, the worm hops to other devices by exploiting system vulnerabilities. If you don’t catch it early, it can slither through your environment and tie up the resources that you need to run your business.
This type of malware’s big break into the mainstream was the infamous ILOVEYOU worm that spread globally in May 2000 by masquerading as a love letter email attachment. Once people opened it, it overwrote critical files and spammed itself to every contact in the victim’s address book, causing plenty of chaos and over $10 billion in damages in the process.
Keyloggers
Keyloggers lurk quietly in the background, recording every keystroke you make. Attackers use them to steal credentials, track communications, or simply gather intelligence. For example, a keylogger might be squatting on someone’s workstation, watching them type in their payroll admin password. Once the attacker has that info, they can slip into the payroll system and reroute funds at will.
Spyware
Spyware is all about covert surveillance. It quietly collects sensitive data like browsing habits, login credentials, or emails, then sends it back to what’s essentially a command-and-control server. Think of it like an expert eavesdropper who’s always listening but rarely leaves a trail. That’s what makes spyware tough to catch, especially if you’re not actively monitoring endpoint behaviors.
Adware
Adware might seem like a lesser threat, “just” cluttering your screen with pop-ups or banners. But don’t write it off as harmless. Malicious adware can open the door to more severe infections if you click the wrong link. It can also slow your network and your productivity. When a random pop-up says you’ve won a gift card and only need to enter your billing info to claim it, you’re seeing one of many examples of malware that thrive on user trust.
Fileless Malware
Fileless malware avoids the usual signs of infection by running in memory rather than installing on your hard drive. It’s tricky because traditional antivirus relies on scanning files. Without a file to detect, the malware can slip under the radar, making it one of the stealthiest types of malware you’ll face.
Cryptojackers
Cryptojacking hijacks your systems’ resources to secretly mine cryptocurrency. You might notice a spike in processor usage or slower performance, but no flashing ransom demands. Attackers profit from your electricity and computing power, while you pay the bill for it. In a large network, cryptojackers can fly under the radar for months, draining resources like digital vampires and jacking up your energy costs.
Rootkits
A rootkit burrows deep into the operating system, giving attackers administrator-level access to do pretty much whatever they’d like. With a rootkit in place, attackers can hide processes, modify system files, or change logs. It’s like handing someone the master key to your building—once they’re inside, they can come and go undetected.
Botnets
A botnet uses infected machines as bots to carry out large-scale attacks. Once your device is compromised, it might barge into thousands of others to spray spam everywhere, launch distributed denial-of-service (DDoS) attacks, or spread more malware. If your device ends up in a botnet, you could get hit with email blacklisting, performance issues, and other unexplained activity.
Not Fun Fact: While 13% of overall incidents were classified as RATs, malware incidents involving remote access were attributed back to RAT malware75% of the time. This highlights their primary role in enabling attackers to remotely control compromised systems. AsyncRAT, NetSupport RAT, and Jupyter were among the most popular variants, accounting for one-third of all RAT types seen in incidents during the year.
