What is "Malware?"
Malware – which is a combination of the words "malicious software" – is a somewhat generic term that encompasses many different types of software which are written to intentionally harm the average computer user. Once a piece of malware is installed on a computer, it can have many different effects, including using the computer to infect other machines through a network or the internet, allowing remote access to the infected computer, the copying of files or keystrokes on the machine, the showing of advertisements, or the sending of spam emails. Hackers and coders make use of malware to perform a wide variety of tasks, and new variants are popping up daily. The prevalence of malware has spawned a massive software industry centered on protecting computers from infection and eliminating these programs once infected. Below we'll look at the most common forms of malware, which every computer user will be familiar with in some way.
Viruses are computer programs that, as the name suggests, have one mission: infect as many computers as possible. Typically viruses will have some sort of "payload" attached – this is another form of malware that causes the majority of the issues for the computer's owner. When the virus program is executed, such as when an email attachment is clicked or a downloaded program is run, the virus will then begin its sequence of trying to copy to other accessible machines. Viruses can range from very minor to nearly impossible to neutralize, and typically cause users a significant amount of grief once their computer is infected. Having an anti-virus program from a reputable manufacturer is the best line of defense against viruses, as these companies focus specifically on tracking down viruses and figuring out how to eliminate them.
Named for the wooden horse that allowed for the conquest of the ancient city of Troy, a Trojan horse (or "Trojan") is a form of malware that looks like a normal piece of software but conceals a piece of malware along with it. The most common form of Trojan is a downloadable piece of seemingly-legitimate software that has some form of spyware (see below) attached to it. The user installs the program and ends up with the other malware installed right along with it. Pirated software found on bittorrent and other sites is also commonly used as a Trojan to get other malware installed on users' machines. It's best to scan any downloaded executable programs with an anti-virus before running them on your machine.
Spyware is one of the most common forms of malware in existence, and rose to prominence alongside the internet. Typically, spyware is designed to collect some sort of information about the computer's users without anyone knowing of its existence. This information is then forwarded on for some form of analysis and use. While simple spyware programs just collect data, there are a few significantly more advanced forms that can cause significant harm and inconvenience to users, and even result in financial losses.
Keyloggers are specific forms of spyware that simply record the user's input on the keyboard and either store it in a file or send it to a remote location. While much of what is typed might not seem to be that valuable to a hacker, if a user types their login details into a site such as PayPal or their online banking interface, the results can be disastrous. Keyloggers are generally very stealthy programs, and can be difficult to even notice, much less remove. Thankfully they are a somewhat uncommon occurrence in the malware world.