What is malware?

The term malware is a contraction of malicious software. Put simply, malware is any piece of software that was written with the intent of doing harm to data, devices or to people. If you are concerned about malware on a website you can use the free Google malware checker tool online.

When you hear talk of viruses, Trojans, spyware and the like, what you're really hearing is talk of different kinds of malware.

We all know the popular image of the rebel hacker, testing his skills and wits against whatever system he's decided to make his challenge. But today, "black hat” software developers often sell their skills to the highest bidder.

These can be criminal organizations looking for tools to operate in the digital world, or government intelligence agencies looking to access the data locked away in the computers, networks and mobile devices of their targets.

Programs supplied officially by companies can be considered malware if they secretly act against the interests of the computer user. An example is the Sony rootkit, a Trojan horse embedded into CDs sold by Sony, which silently installed and concealed itself on purchasers' computers with the intention of preventing illicit copying; it also reported on users' listening habits, and unintentionally created vulnerabilities that were exploited by unrelated malware.

What does malware do?

The way malware goes about doing its damage can be helpful in categorizing what kind of malware you're dealing with. The following is a list of common classes of malware, but it's hardly exhaustive:

• Virus: Like their biological namesakes, viruses attach themselves to clean files and infect other clean files. They can spread uncontrollably, damaging a system’s core functionality and deleting or corrupting files. They usually appear as an executable file.
• Trojans: This kind of malware disguises itself as legitimate software, or is included in legitimate software that has been tampered with. It tends to act discretely and create backdoors in your security to let other malware in.
• Spyware: No surprise here: spyware is malware designed to spy on you. It hides in the background and takes notes on what you do online, including your passwords, credit card numbers, surfing habits and more.
• Worms: Worms infect entire networks of devices, either local or across the internet, by using network interfaces. It uses each consecutive infected machine to infect more.
• Ransomware: Also called scareware, this kind of malware can lock down your computer and threaten to erase everything — unless a ransom is paid to its owner.
• Adware: Though not always malicious in nature, particularly aggressive advertising software can undermine your security just to serve you ads — which can give a lot of other malware a way in. Plus, let’s face it: pop-ups are really annoying.
• Botnets: Botnets are networks of infected computers that are made to work together under the control of an attacker.
• How do you remove malware?  

Each form of malware has its own way of infecting and damaging computers and data, and so each one requires a different malware removal method. Avoiding suspicious emails, links or websites are good online habits to have, but will only get you so far: attackers can sometimes compromise even legitimate websites.