This is the very real world you live in.
A war is raging on and you don't even know it.
The fact that there are so many terms for these types of infections brings about mass confusion, resulting in end-users who are either overly worried or dismayed to indifference. To top it all off, it's a battle you will never win, resulting in distrust of antivirus applications and perceived ineffectiveness of all solutions you try implementing. As new technology arrives, and more importantly, as it becomes popular, it becomes a new target. As new security measures are introduced, there are individuals and companies spending inordinate amounts of time and money to beat it.
Ok - but why?
The answer varies. Some of it is written to be just cruel and evil, where the creator finds happiness in wreaking havoc. The same could be said for many criminals. However, in those instances the software is commonly a virus (malicious software that can reproduce itself by spreading to other machines). This is just a small percentage of the evil lurking in the shadows. It is, however, purely monetary greed that is fueling the perpetuation of the many forms of malware (software infiltrating your computer without your consent or knowledge) that plagues most computers.
Spyware simply watches what you do. The gain is had by aggregating the information for marketing benefits, but spyware (and other malware) can also track every key you type on your keyboard, including credit card numbers and passwords.
Scareware usually arrives as a surprise urgent notice that is entirely without merit, yet craftily legitimate in appearance, scaring you into making a purchase that you don't need and will gain no benefit from. Clicking anything, including the exit, close or no thanks button is exactly the same as clicking the yes button. Advice: Halt all the iexplore.exe processes. If you don't know how, just shut your machine down.
Adware, which deserves a special section of its own, is software that employs a multitude of tactics to display advertisements (from which they benefit). Often, the manner in which the adware is shown to you is done in such a way that you don't even realize it. For example, some adware will literally replace images on websites with their ads. So while you believe you're looking at the real website, you're actually looking at an altered version directing any possible sales their way. Another method is redirecting your internet browsing, replacing the web page you see with their own crafted page (which is then commonly infected with further malware variants). This redirection process may be completely transparent to you, where the URL you type in looks legitimate. All this, to drive where and how you spend your money online.
Trojans are software that looks like legitimate software, but harbor malicious intent. Trojans look and act like they are doing something you want or like, but are really doing you or your computer harm - in many cases it's used as a tool that opens a backdoor to your computer, giving the creators remote access to your computer. I'm sure you're saying to yourself, right about now, that's never happened to me! If you are one of those happy-go-lucky internet web surfers who constantly has "clean-up" work needing done, you can just about bet your system has been access remotely. In most cases the remote attacker wants to utilize your system to send spam, or they are using your system as a middle machine to gain access to other machines permitting them to remain "stealthy” or worse yet, they want your documents containing credit card numbers and passwords.
Clarification - Well we shall try, anyway.
So, just to clarify the basics here, lets cover all of those terms briefly.
Viruses - Malicious infection that has the ability to reproduce and spread (for simplicity sake - a worm is a virus).
Malware - Malicious software installed without your knowledge or intent.
Trojans - Seemingly legitimate software, with hidden and malicious intent.
Adware - Software bent on showing you what they want you to see.
Scareware - Software using manipulation to sell you something.
Spyware - Software watching what you do, where you surf, and/or every letter you type on the keyboard.
You should note these can be interrelated in their deployment methods. You can mix and match them together. Thus, one infection opens you up to a plethora of new infections. For instance, you could surmise that spyware can be installed by a trojan, that was installed without your consent when you purposefully installed that latest greatest screensaver. And yes, searching for screensavers online is like walking into a closet filled to the top with scorpions and then expecting to not be stung.
Worms are very much like a virus, in that they spread from one system to another. The difference between them is minor from and end-user perspective. For the sake of end-users everywhere, let’s just presume viruses and worms are the same thing.
Your Problem - Real-Time Protection
One problem is that many Antivirus software applications do not protect you from all these various forms of infections. You might buy a virus protection application, but forgot to get the malware module. Or, you may not have it configured properly. If it's not scanning every single accessed file, all the time, then your computer will sit there, infected, until you perform a scan - a day late and dollar short. Even if you're a magical wizard on the computer and you've got all the modules running, you good sir, are not safe. Variant malicious software comes out new every day, yet to be identified by your wonderful tools.
Fighting the battle - In order of importance
1.) First, and most importantly, you'll need a battle suit - and I've got one, made of gold, just for you. Whether you wear this armor, or not, is your call. Though, I can tell you now that you won't wear it. Here it is, get ready to put it on: Stop surfing the internet like a kid in a candy store. Stop opening forwarded emails from your friends that tell you that Bill Gates will give you $100 if you click this link. Stop opening up documents from the fake post office. Stop going to MySpace. Stop opening emails that say "URGENT" or "IMPORTANT" or "YOU'LL LIKE THIS" or "FACT" or "TRUE STORY". Come on now, are you really that gullible? The fight starts with you. If it's too good to be true, it's probably not. If it quacks like a duck..
2.) Get an Antivirus Application with real-time protection and an anti-spyware, anti-adware, anti-malware module. The problem with my next suggestion is that it will not last. The program I'm about to recommend will eventually, and all too soon, become obsolete (just like Symantec is now, and just like AVG is on its last leg). Go buy ESET Nod32 Antivirus 4 ( http://www.eset.com/home/nod32-antivirus ). Some of you may already have a purchased copy of Symantec - Please, do yourself a favor - get rid of it. If you're using AVG, free version or not, you may as well make the switch now. Why? Good question. Because there is a lot of malicious software written to specifically get around it, or worse still, look and act just like it. I figure ESET has another year before it becomes the target of choice. Obviously, whatever AV application is the most popular will see more software written specifically to beat it. On the other hand, I'm specifically slapping Symantec because not only is their software very easy for bad software to get around, it is also bloat-ware (software that is so full of compounded code over years of development that it can bring a fast running computer to its knees).
3.) Scan often. Most users live in this magical world where they believe that once an Antivirus application is installed, it will work magic wonders all on its own. Sure, real-time-protection is groovy keen, but you MUST also scan. Configure your application to scan at regular intervals. And finally, don't get complacent. If you're not seeing infections during the scan, don't stop doing them. Your methods are working, keep it up.
I hope that I've helped you understand the differences between all these terms, and helped to guide you to better online protection. However, If you need any assistance cleaning up the mess you got yourself into, I'll be there. I say this because my computing is now 15 years without an infection - but I've cleaned up a thousand of other people's computers. At the time of this writing - the most common threats I've seen are from File sharing applications (stop using LimeWire please) and scareware (false infection alarms - clicking anything causes infection). The most common newcomers gaining momentum are infected PDF files, and Facebook apps.