First off, a virus is defined as malware that is self-replicating, which means it copies itself when executed. There are four typical methods that a virus takes to infect your computer. A resident virus will install itself into the operating system and run every time the computer boots. A non-resident virus will scan the hard drive and infect files. A macro virus will be attached to another file, such as a Word document or PDF file, and be executed when you open the infected file. Finally there are boot sector viruses that infect digital media like hard drives, flash drives, etc.
A Trojan is generally a non-replicating form of malware that is designed to give someone else access to your computer without your knowledge. They are often disguised as legitimate or helpful programs in order to gain this access. Trojans may be acquired through email attachments or “drive-by-downloads,” where a compromised website clandestinely downloads the file to your computer.
A worm is malware program designed primarily to infect multiple computers by creating a cyber “pathway” by which other infections can be quickly spread. Worms create the “backdoor” through which a Trojan or virus can enter, but the devastating effect can be vast as the worm has already weakened the structure for the other malware to work destruction more easily.
Ransomware is malware that prevents you from using your computer or accessing files, unless you pay a ransom to release the lock. Some famous examples are the FBI Virus and Cryptolocker. Ransomware typically attacks via a Trojan or worm and then sets about restricting access to areas of your computer. Sometimes, ransomware will even attempt to scare or threaten you with supposed legal consequences, as in the case of the FBI Virus, or it may simply tell you that you can’t access your files until you pay X number of dollars. Encrypting ransomware such as Cryptolocker is very damaging, as there is no decryption key unless you pay the ransom.
Adware is short for advertising-supported software. Adware essentially pesters you with advertisements for a product in the hope that you will purchase it. Think of it as the salesman who won’t leave you alone. Some adware is legitimate, this is usually seen when you download a trial version of a program or perhaps a “free” piece of software. The program might be free to you but the person who wrote it still needs to earn income, this is done by selling advertising rights to other companies.
Spyware, as its name implies, is used to spy on you. While spyware can be used to monitor system activity it is primarily used to gather information about the user and their habits, such as what websites they visit, what programs they use, how long they use the computer, etc. Tracking cookies, one form of spyware, are typically used by companies and advertising agencies to track web users. These cookies monitor where that user has gone, how long they stayed there and what else they clicked on. All of this (and other) information is then utilized to customize ads to that user. This is one way a website appears to know your name, or that you were looking for new boots. Sometimes companies are up front about their use of tracking cookies, many times they are not.
This list is meant to be a summary of common computer infections, but is by no means exhaustive. The effects of malware infections are numerous and not always obvious. Some malware is truly harmful and malicious, while other malware is simply irritating or slows down your computer. Typical signs of infection are reduced system performance, error messages, popups, getting redirected to other web sites online, slow Internet, programs locking up or random activity. It is important to make sure your software is up to date and that you have a solid security suite running to keep you safe.
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