Differences between viruses, worms, trojan horses, spyware, adware, dialers and scumware

What are the differences between viruses, worms, Trojan horses, spyware, adware, dialers and scumware?

We all know that modern virus scanners (usually) do a pretty good job in protecting our PC’s. Even though we generally don’t care how they work, most of us tend to wonder what that ‘thing’ was the virus scanner just found and deleted.

If you have so far been thinking that every threat you encounter on the Internet is just simply a ‘virus’ it may be time to reconsider. There
are hundreds of new threats created every month that roam through the net in search of hapless victims.  Someday you might be on the receiving end.

To even remotely be able to fight all these new threats every month they need to be properly categorized and analyzed before they can be

Today’s environment discerns between many types of threats most of which can be placed in any of the categories below. What once simply was a ‘virus’ now can be classified as anything from a worm to a trojan horse.

Identifying what category of viruses there are is the keystone to successfully protecting your computer from all these threats. Most
people have a virus scanner and a firewall installed. But while we think ourselves safe behind our powerful defenses, our computers slowly fill up with all sorts of unseen and unwanted ‘evil’ not blocked by our firewalls and virus scanners.

The following is the primary list of hazardous categories that you may encounter while surfing the Internet.  By no means is it 100% complete nor are they the only threats that might cause damage to your computer (and possibly your sanity when you lose all of the data you never had the time to back up!), but they are the main categories.

Trojan Horses
Hacking tools

The classic computer virus is aptly named after its natural counter part. Take for example the ever-present flu virus. You can encounter it
practically anywhere in the world and it easily spreads through contact which can be extremely hard to avoid.
Computer viruses behave much in the same way. Computer viruses will attach themselves to programs and spread to other programs by inserting themselves into that program. A lot of viruses simply only replicate themselves in this way, but will generally do this at an extremely fast pace. A typical ‘symptom’ of a virus that simply replicates would be computer slow-downs and eventually regular crashes up to the point of the PC being unable to run at all.
Some viruses not only ‘infect’ other programs, but also cause those programs to behave erratically and/or fail which generally results in
unrecoverable information on your PC. (Ouch!)  If the affected information is critical to the operation of your PC (like parts of your
operating system) it will generally lead to the loss of all data (or at least a substantial amount) on your computer.


The worm is similar to a virus in the way that it also spreads. The difference here is however that the worm is capable of copying itself
rather than relying on other files or programs to help it spread.
Worms are generally capable of copying themselves from something like a floppy or USB “pen” drive to a hard disk but will also use another medium (e.g. email) to send themselves to other computers.
Worms like viruses can do extensive damage to the information on your PC but can also be used to compromise your system and open it up to other attacks.
This means that the effects of a worm may not always be visible but simply may result in (for example) your firewall or virus scanner not
behaving properly.
Worms generally have to rely on disguising themselves as other programs to be spread. Typically an email with some sort of entertaining program (a little game or a screensaver) serves as cover for these insidious programs.

Trojan Horses

The balance of threats on the internet has slowly shifted from classic viruses to what is now known as a ‘trojan horse’ (trojans) or backdoor
Trojans generally don’t replicate or spread themselves in any way, shape
or form but have proven to be one of the greatest threats to your computer.
A trojan horse is used to create openings in the defenses of your computer allowing other people to access your system. This means that
anyone who would be interested could access your PC, look at or delete your files and even introduce viruses and worms on your computer.
Trojans are generally used to introduce hacking tools on your system which are discussed later on in this article.
A trojan is rarely noticed until it is too late and more often than not will never cause damage to your system but instead be used to spy on
your activities.
Trojans, like worms, generally camouflage themselves as harmless programs that are spread through emails and other means and can sometimes be the payload (part of) a worm.


Spyware programs are programs that are used to spy on any sort of activity on your computer. This type of program is particularly intended
to retrieve private or personal information and transmit this information to the owner of the tool.
Spyware programs rarely are destructive nor intended to compromise security any more than they have to. Naturally having your personal data (like credit card information!) and passwords spread all over the web can be a greater threat than any worm or virus could ever be.
Spyware programs can be inadvertently downloaded from web sites or be activated by accepting user license agreements attached to other
programs.  (Note to self:  Always read before clicking a popup!)
It is important to note that spyware is generally not detected by most virus scanners or blocked by firewalls (since you ‘kind of’ agreed to
download the software). As a result care must be taken to prevent your personal information from falling into the hands of strangers.


Adware programs are generally introduced on your system in the same way as spyware and may even accompany spyware. Unlike spyware, adware is mostly concerned with your browsing habits and will transmit information about your day to day activities online to a remote computer. This information is then used to display appropriate ads (pop-ups or otherwise) to you which are intended to generate income for the owner of the program.
This makes adware programs slightly more tolerable. Since there are very few ways to distinguish between spyware and adware programs they should both be removed for the purpose of safety.
Like spyware adware requires specialized tools to be detected and removed from your PC.


Scumware is often referred to as adware, but rather than displaying ads to you the program is designed to ‘steal’ income away from legitimate sites by hijacking links. Every time you click on an ad from a seemingly legitimate site scumware will cause that link to be redirected through one of the scumware servers. Since every click on the internet can be potential income scumware is very effective in crippling the marketing efforts of legitimate web site advertisement.
Scumware is distributed in the same way as spyware and adware and is often accompanied by either of the two.
Scumware even though it doesn’t pose a threat to your own system in general should be dealt with to ensure that your money goes where you intended it to go.


Dialers are often a problem for people who use their phone line as main internet connection. A dialer is intended to ‘dial-in’ to other sites
without your knowledge making use of your phone line. This is generally intended to build up charges and will often result in extremely high phone bills.
Dialers will not harm your system in any way since this would decrease their effectiveness.
Dialers can be downloaded accidentally from web sites or may pose as seemingly harmless programs. Once again specialized tools are required to remove these dialers as most virus scanners may not identify a dialer as a potential threat.
Dialers generally only pose a threat to people that use their phone line for their internet connection. Even though there are some dialers that will affect cable users those of us lucky enough to be online via cable will generally not need any protection against these programs (deletion is nonetheless recommended).

Hacking tools

Hacking tools are generally not considered to be a virus. Introduced into your system by email or any other means of transport (maybe even a disgruntled friend or colleague) these little tools are full-fledged programs that can allow any number of things.

A typical example of a hacking tool would be the so-called ‘keystroke logger’ which stores everything you type including passwords and other critical information.


Outside the boundary of all threats there’s a large grey area which we will just call ‘nuisances’. A nuisance can be anything from an annoying screensaver that keeps popping up whenever you don’t want it to your web browsers start page being changed by some external means.

These kinds of nuisances are usually not a threat and are often very creative and even amusing. A virus scanner will generally detect these
and remove them long before you are ever cursed (or blessed, if you are bored) with their presence.

Now that you are familiar with the general categories of the threats commonly found today you should be well equipped to find an appropriate solution to your problems. Hopefully you will be able to secure yourself well enough to never have to worry about internet problems again.

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