What is a Malware?
Malware is a general term. It also means malicious software, which is literally any software that means no good once it infiltrates your system. A Malware is a computer program created and propagated to damage computer systems and steal important information from you. Actually, malwares are made to perform a certain task that would benefit the malware maker (such as monitoring your Internet activity). The nasty effects that the malware brings to your system are often because it was designed solely for something without considering the side effects it can bring to the computer system.
The first malware was the Creeper virus (early 1970s) which is an experimental self-replicating program created by Bob Thomas. It was detected on ARPANET, which is said to be the early edition of the Internet. It spread via the TENEX operating system. Once it infected a system, it would display the message, “I'M THE CREEPER:CATCH ME IF YOU CAN." The Reaper program was then created by the same author to detect and destroy the Creeper virus.
What is the difference between a computer worm and a computer virus?
Actually, people say that worms are viruses but the truth is they are not. They do contain a lot of similarity to each other, but they are two different things. Viruses need human intervention to propagate. They often reside to .exe files (so be careful with unknown .exe files), or executable files. Once you clicked it to run, the virus would be launched on your system. Much software such as those who offer services like to crack a certain application has some viruses in it. Furthermore, those that offer patches that promises to upgrade illegally a software to premium for free is pretty much virus launching softwares. Don’t you dare to be persuaded by those people. You might think you are just cracking a certain software to make it premium but on the background you might have executed a computer virus. Such frauds and scams are spread across the web. Worms, on the other hand, are self-propagating and can be self-replicating malwares. Once your system is infected by a worm it would propagate itself without the need of human intervention. The scary thing about this malware is it can replicate itself, increasing itself inside your system and possibly replacing and corrupting any document inside your computer. Worms spread wildly on the Internet, when you're infected PC is connected to another PC the worm would eventually find its way to the other computer. Since they replicate so much inside your computer, worms slow down your computer, add more its ability to access the Internet and hire some other malwares (well it depends on how the malware was programmed, there are some malwares that are meant to disable your computer’s defenses in order for a much nastier virus to infiltrate your computer system).
What about Trojans?
Remember the story of the Trojan War? A story from the Greek mythology, wherein the Greeks or Achaeans wage war against Troy because Paris the king’s son took Helen the wife of Menelaus king of Sparta, remember the horse there? The Greeks's wooden horse or the Trojan horse was made as offering for the Goddess Athena. The Trojan horse that has thirty strong Greek soldiers concealed inside it, was dragged by the Trojans inside their city. That careless move by Trojans brought them to their fall. Just like the story a Trojan is simply some application or software that seems to be good at first, but once it gains a grip inside your system, it would do some nasty things.Many times it disguises itself as free software that promises a service similar to a known premium one. And before you know it, the Trojan infiltrated your system. Good, if your antivirus detects it but of course your antivirus cannot detect every malware. So be careful in downloading stuffs in the web, much to those that offer themselves for free. Trojans like to disguise themselves as a very useful software that offers itself without charge. By the definition, Trojans are viruses since you need to execute them manually in order for them to function.
What is a Spyware?
Spywares are Malwares that tends to spy on your system. It secretly collects information about the users. This kind of malware is capable of stealing your username, passwords, account passwords, etc. One common type of a spyware is keyloggers. Keyloggers are software that can be installed inside your system to detect keystrokes. If my computer has one installed inside right now, my whole article would appear in the keylogger along with my email username and password. Of course it depends on how good the created keylogger is (if it could distinguish between words from an article or be it programmed to copy only my usernames and passwords of any sites I am signed up into). Furthermore, Spywares are also used to view people's browsing activities. Nasty marketers use this kind of malware to know the interest of the users, what would they want to buy, what service they desire, etc. After acquiring that information they would either bombard you with pop-ups ads (usually called Ad wares), spam your mails with items they want to sell, or they can do both.
What is a Crimeware?
Crimeware (coined by Peter Cassidy, Secretary General of the Anti-Phishing Working Group) is a software that used to promote cyber crimes. Both Spywares and Trojan are examples of this. Simply combining the definition of the two (spywares and Trojans) would yield to the definition of a crimeware. Such programs are used for online theft, stealing accounts or even redirecting your browser to a certain site (such as malwares that redirects you to a certain site are called hijackers).
What is an Adware?
Adware, short for advertising-supported software, is a software that displays an advertisement to a computer, often in the form of “pop-up” ads. Actually there are times that Adware is not classified as a malware. Usually such kind of software is installed with the user's consent. There are softwares that once you download, it would prompt you to install an adware (and we often just click “OK”, often seen on softwares that installs browser toolbars, might as well avoid those kinds of softwares ). However, some Ad wares can be classified as a malware. If you haven’t subscribed to any ads or don’t have any knowledge that you have downloaded a certain software that prompts you to install an adware better check your system now.
What are Rootkits?
Rootkits are malware that is hidden inside an infected computer, and it is made to be undetectable by antivirus software. Once your computer is infected the rootkit virus would not abruptly meddle with your system, it slowly infects or attaches itself to your system files (sometimes they rename themselves to look like good files, disguising themselves to avoid being detected by your antivirus). This malware is known to disarm your antivirus and download other malware (commonly spywares) once it infiltrated your system. This would make you vulnerable to phishing attacks. There are softwares that are specifically made against rootkit viruses, AVG Anti Rootkit is one example.
What about a Retrovirus?
Retrovirus is another kind of malware designed to attack directly the anti-virus installed inside your system. It is an anti-antivirus. It can be a software that tricks the user to uninstall their antivirus or make the installed antivirus inoperable by corrupting its virus signatures (also known as Bounty Hunter).
Other kinds of malware:
- Boot viruses
References: Wikipedia.org and Kioskea.net