10 Types of Malware You Need to Know About

Malware is a word that gets thrown around a lot lately, no thanks to the 600% uptick in cybercrime ever since the COVID-19 pandemic started. In the healthcare industry, it’s a word we hope we never have to hear because we know it’s only going to bring bad news.

But what is malware? And what types of malware should we be wary of?

What is malware?

Malware, shorthand for malicious software, is the collective name for software designed to compromise, cause damage, or gain unauthorized access to a computer, server, or network. They are created to exploit devices at the expense of the user and to the benefit of the hacker.

Malware can steal, encrypt, or delete data, hijack core computing functions, as well as monitor the computer activity of users.

Common Types of Malware

Now that we know what malware is, it’s important to keep in mind that malware is a very broad term and that there is a wide variety of malicious programs that fall under it.

And because you need to know them so you can better avoid them, it’s important that you’re familiar with the common types of malware.

Here are 10 common types of malware—some you may remember hearing about in the news many years ago, and some you should still keep an eye out for today.

File Infectors

A file infector is a type of malware that generally copies its code into executable programs such as .com and .exe files. When a corrupted file is run, the virus replicates the malicious code, spreads it to other executable applications on the computer, and, in the process, sometimes damages the host programs. 

The Cascade virus was a widespread file infector from the 1980s to the 1990s. It infected .com files and its effect was making text on the screen cascade or fall down, forming a heap of text at the bottom of the screen.

When an infected file is introduced to a system and executed, the Cascade virus checks the BIOS for the string COPR. IBM. If it finds the string, it will try to stop there. However, it will not be able to do so, and this is when the virus becomes memory resident. Every time a .com file is run, the virus begins to infect it.

The Cascade virus is almost extinct nowadays.

Stealth Viruses

A stealth virus is a type of malware that conceals the changes it makes by hijacking certain system functions. It hides in your system memory whenever a program scanner is run. When other applications request data from portions of the system modified by the virus, the infection reports back the accurate, unchanged data, instead of the malicious code.

The Brain virus, the very first DOS virus, was a case of stealth infection. It was discovered in 1986 and was aimed at the IBM PC. When an infected disk was turned on, the virus installed itself into the memory and took up space. It did not infect the hard disk, but infected any other floppy disk accessed while it was in memory.

The Brain virus’s stealth capabilities came into play any time infected sectors were accessed. It redirected the accessing program to the stored original boot sector, and this made it undetectable to early disk utility tools.

The Brain virus is believed to be extinct.

System or Boot-record Infectors

A system or boot-record infector is a type of malware that attaches to a small program known as the boot record, which is run when the computer starts up. Starting up the computer using the infected disk will automatically execute the virus-infected code. Once your computer has been infected, any unprotected floppy disk put into the computer will also be infected.

The Michelangelo virus was a boot-record infector first discovered in 1991. It infected the boot sector of floppy disks and hard disks. By moving the master boot record to a different section of the hard disk, the infector replaced the original master boot record with an infected one.

The Michelangelo virus infected all the floppy disks used in the infected computer that were not write-protected. When activated, it also overwrote some part of the information included in the hard disk, which meant losing approximately 8 MB of data. 

Though there are still infected diskettes existing in the world, the Michelangelo virus is largely extinct.

Macro Viruses

A macro virus is a type of malware that is written in the same macro language as the software it infects. It is commonly found embedded in documents attached to emails or inserted as malicious code into word-processing programs. Macro viruses typically affect Microsoft Excel and Microsoft Word, and can affect both PC and Mac computers.

The Melissa macro virus was a mass-mailing malware that took over users’ Microsoft Word programs, and then hijacked their Microsoft Outlook email accounts to send emails that contained infected attachments. 

Although it wasn’t designed to steal money or data, the Melissa macro virus was able to overload email servers, disrupt email accounts, and slowed Internet traffic in certain places around the world.

At present, variants of the Melissa virus still roam the Internet.

Worms

A worm is a type of malware that can replicate and spread itself on a network or system without the need for user interaction (e.g., opening a file, running a program, etc.). A worm can modify files, delete data, and even inject malicious software onto your computer. However, there are times when a worm’s purpose is to overload a network or deplete a computer’s resources by making copies of itself over and over.

The Nimda worm was first discovered in 2001 when its worldwide outbreak led to the shutting down of Internet sites all across the globe. It targeted Windows-based computers and servers. Though it did not damage hardware, the Nimda worm significantly slowed down Internet traffic and email access by clogging them with junk. 

Unlike most worms of its time, which spread through email attachments, the Nimda virus could be caught just by visiting an infected website. Cybersecurity experts have described it to be the fastest-spreading computer virus at the time.

Several variants of the Nimda worm exist and may still be around to this day.