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Types of malware explained

It's important to get your malware classifications straight because knowing how various types of malware spread is vital to containing them. With VortexShield you can rest assured that we will keep your computer safe from all kinds of malware and threats. Learn more at


A computer virus is what most of the media and regular end-users call every malware program reported in the news. Fortunately, most malware programs aren't viruses. A computer virus modifies other legitimate host files (or pointers to them) in such a way that when a victim's file is executed, the virus is also executed.

Pure computer viruses are uncommon today, comprising less than 10 percent of all malware. That's a good thing: Viruses are the only type of malware that "infects" other files. That makes them particularly hard to clean up because the malware must be executed from the legitimate program. This has always been nontrivial, and today it's almost impossible. The best antivirus programs struggle with doing it correctly and in many (if not most) cases will simply quarantine or delete the infected file instead.


Worms have been around even longer than computer viruses, all the way back to mainframe days. Email brought them into fashion in the late 1990s, and for nearly a decade, computer security pros were besieged by malicious worms that arrived as message attachments. One person would open a wormed email and the entire company would be infected in short order.

The distinctive trait of the worm is that it's self-replicating. Take the notorious Iloveyou worm: When it went off, it hit nearly every email user in the world, overloaded phone systems (with fraudulently sent texts), brought down television networks, and even delayed my daily afternoon paper for half a day. Several other worms, including SQL Slammer and MS

Blaster, ensured the worm's place in computer security history.

What makes an effective worm so devastating is its ability to spread without end-user action. Viruses, by contrast, require that an end-user at least kick it off, before it can try to infect other innocent files and users. Worms exploit other files and programs to do the dirty work. For example, the SQL Slammer worm used a (patched) vulnerability in Microsoft SQL to incur buffer overflows on nearly every unpatched SQL server connected to the internet in about 10 minutes, a speed record that still stands today.


Computer worms have been replaced by Trojan horse malware programs as the weapon of choice for hackers. Trojans masquerade as legitimate programs, but they contain malicious instructions. They've been around forever, even longer than computer viruses, but have taken hold of current computers more than any other type of malware.

A Trojan must be executed by its victim to do its work. Trojans usually arrive via email or are pushed on users when they visit infected websites. The most popular Trojan type is the fake antivirus program, which pops up and claims you're infected, then instructs you to run a program to clean your PC. Users swallow the bait and the Trojan takes root.

Trojans are hard to defend against for two reasons: They're easy to write (cyber criminals routinely produce and hawk Trojan-building kits) and spread by tricking end-users — which a patch, firewall, and other traditional defense cannot stop. Malware writers pump out Trojans by the millions each month. Antimalware vendors try their best to fight Trojans, but there are too many signatures to keep up with.


Malware programs that encrypt your data and hold it as hostage waiting for a cryptocurrency pay off has been a huge percentage of the malware for the last few years, and the percentage is still growing. Ransomware has often crippled companies, hospitals, police departments, and even entire cities.

Most ransomware programs are Trojans, which means they must be spread through social engineering of some sort. Once executed, most look for and encrypt users’ files within a few minutes, although a few are now taking a “wait-and-see” approach. By watching the user for a few hours before setting off the encryption routine, the malware admin can figure out exactly how much ransom the victim can afford and also be sure to delete or encrypt other supposedly safe backups.

Ransomware can be prevented just like every other type of malware program, but once executed, it can be hard to reverse the damage without a good, validated backup. According to some studies, about a quarter of the victims pay the ransom, and of those, about 30 percent still do not get their files unlocked. Either way, unlocking the encrypted files, if even possible, takes particular tools, decryption keys and more than a bit of luck. The best advice is to make sure you have a good, offline backup of all critical files.


If you're lucky, the only malware program you've come in contact with is adware, which attempts to expose the compromised end-user to unwanted, potentially malicious advertising. A common adware program might redirect a user's browser searches to look-alike web pages that contain other product promotions.


Spyware is most often used by people who want to check on the computer activities of loved ones. Of course, in targeted attacks, criminals can use spyware to log the keystrokes of victims and gain access to passwords or intellectual property.

Adware and spyware programs are usually the easiest to remove, often because they aren't nearly as nefarious in their intentions as other types of malware. Find the malicious executable and prevent it from being executed — you're done.

A much bigger concern than the actual adware or spyware is the mechanism it used to exploit the computer or user, be it social engineering, unpatched software, or a dozen other root exploit causes. This is because although a spyware or adware program’s intentions are not as malicious, as say, a backdoor remote access trojan, they both use the same methods to break in. The presence of an adware/spyware program should serve as a warning that the device or user has some sort of weakness that needs to be corrected before real badness comes calling.

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