Types of Viruses
Adware: Adware is among the most troublesome of computer threats. It can hide in places such as downloads for songs, movies, etc. Once installed on your computer, adware creates a flurry of advertisements and sends them directly to your computer. They can embed even more advertisements within the text of articles.
Boot: A boot sector virus is a line of code that affects the boot sector of your computer. It is transferred from one computer to another via USB drives. The boot virus can prevent your computer from starting up or make it impossible to locate its hard drive. If your computer has ever shown a blank blue screen, commonly known as the "Blue Screen of Death," you've probably been the victim of a boot sector virus.
Bug: A bug is any kind of fault or flaw in a computer program that stops it from functioning correctly.
Direct Action: Direct action viruses begin their work as soon as they are installed on your computer. Typically, direct action viruses are designed to immediately activate/replicate when someone performs a specific action on a computer.
Directory: As its name would suggest, a directory virus attacks your computer by infiltrating its directory. (In computer terminology, a directory is just any big computer file that contains several smaller sub-files.) Typically, it will infect files with .EXE or .COM extensions. Invisible to the user, a directory virus changes the host file so that the virus activates with the host file.
File Infector: File infectors are a classic virus; when someone refers to a generic virus, they are probably discussing these. These viruses spread from program to program by seeking out files to infect and then copying code into those files. Eventually, if left unchecked, file infectors can take over an entire system by compromising all of its files.
Hijacker: Hijacker viruses alter your Internet browser settings, typically in order to force your browser to redirect you to a page specified by the virus. These redirect pages are usually designed to advertise a product or drum up publicity for something/someone. They also alter the home page of your browser, spam you with unwanted advertisements, and block you from viewing Internet content.
Keylogger: Keyloggers place hidden software on your computer. This software keeps track of your keystrokes and takes note of the passwords you enter. Depending on what accounts you have, this can give hackers access to all kinds of private information.
Macro: Macro viruses contaminate individual programs on your computer. When a macro virus infects a program, it triggers a series of actions that will happen whenever someone runs the program.
Malware: Malware is any computer code that is designed to infiltrate a computer and damage it or its content.
Overwrite: Overwrite viruses attack files/programs on your computer and make them unusable. They can also be extraordinarily dangerous to your computer. If left unchecked, they can crash your computer entirely and prevent it from booting back up. If a file/program on your computer has been attacked by an overwrite virus, delete the damaged file. As this is the only way to remove an overwrite virus, it's wise to keep backups of your important files so you can delete them without trouble if necessary.
Phishing Scam: Phishing occurs when you receive an email from a seemingly legitimate source asking for personal information like your Social Security Number or credit card number. Legitimate companies will never solicit this kind of information via email. If you receive an email asking for this information, delete the email immediately and report it to your system administrator.
Resident: Resident viruses "make a home for themselves" by storing themselves within the memory of your computer. Since the virus is not attached to any one file, uninstalling it can be very difficult.
Spam: The term "spam" refers to emails sent with the intent of advertising something or getting you to click a link. At their best, spam emails are simply nuisances that clutter your inbox, and they can be dealt with by dragging-and-dropping the spammy message into the recycle bin. At their worst, they can promote illegal products/activities or conceal malware.
Spyware: Spyware is a form of malware that spies on your computer use. Spyware can take screen shots, capture data such as passwords and usernames, and collect other personal information. Keyloggers are just one example of spyware.
Trojan Horse: A Trojan horse is a virus that hides inside of something to make itself look enticing and appealing.
Virus: A virus is a type of malware that is designed to replicate and spread.
Worm: A worm is a form of virus that can copy itself and spread from computer to computer. It is not downloaded or attached to any one program; rather, it tunnels through computer networks in order to spread.
Check out the articles Antivirus Software Tips and Mac Viruses & Tips.