All viruses, trojans, malware, adware, spyware, and phishing are malicious - they are bad for you and your computer. They all have the goal of stealing your information, taking over your computer, or trashing your computer (sometimes all of those).
Malware is a generic word to describe all forms of software designed to steal your information, take control of your computer, grant unauthorized access to your computer, or damage your computer.
Viruses in computers are much like biological viruses - they spread easily. A virus is hidden in a file, and when you execute or run that file the virus starts to replicate itself throughout your hard drive, once this happens, the affected areas are said to be "infected". Viruses can slow down your system, access and corrupt data, create spam, or log your keystrokes. Viruses often use complex anti-detection or stealth strategies to avoid being removed by antivirus programs. If even one infected location is left on your computer, the virus will continue to self-replicate as if it was never removed.
Trojans, or trojan horses, are similar to viruses but they don't self-replicate. Instead they masquerade as a legitimate file, and try to get you to run them. When you do that, a trojan will create a "back door" into your system and "call home". After that, the hacker can access your system whenever they want without your permission or knowledge.
Adware, or advertising-supported software, is any software which automatically renders advertisements to generate revenue for its creator. Malicious adware presents unwanted advertisements to you. One example of this are pop-ups. Adware can vary from being an annoyance to being a serious threat - depending on how hard it is for you to get your work done.
Spyware is software that gathers information about your system and users without your knowledge. It then sends that information to another group or person for them to use. Often spyware is included as part of valid software that you install that comes from a malicious website.
Phishing is different from the other forms of malware listed. It is a form of social engineering using email. Examples would include unusual e-mails asking for some form of personal or confidential information. That is a phishing email. Spear phishing is believable and targetted - possibly appearing as an email from your work company or other legitimate source.
To help you against all forms of malware, there are 3 rules:
- Install a good antivirus program, keep it updated, and run it regularly. For more information, see How can students protect their computers from viruses?
- Do not reply to an email from someone you don't know. If the email wants you to click a link, check the URL. Is it actually who it says it is?
- Do not open a file you do not know, or that comes from someone you do not know.