Malicious Intentions The Virus Worm Trojan

Health IS Technology Blog

Malicious Intentions: The Virus, Worm & Trojan

"Like the castle-dwellers of old, computer users are involved in an arms race with hackers and virus writers. This makes it imperative to understand the types of computer threats that may affect school and classroom computers and networks." (The Journal)

Woman sitting at computer frustrated

Sound Security

It’s very likely that you along with millions of other individuals, public organizations and private businesses across the globe have at some point, been impacted by a malicious computer threat, such as the infamous computer virus, worm or trojan. These threats amount to billions upon billions of dollars for necessary repairs, lost or corrupted data, identity theft, etc. In one report, “Computer Economics estimated the worldwide cost of CodeRed and CodeRed II, related blended threats that launched DOS (e.g. disk operating system) attacks, defaced web servers and left trojan horses behind for later execution, at $2.62 billion dollars.” (Webopedia)

Despite all of this, many people are still unfamiliar with exactly what these malicious programs are and the key differences between them. Keeping your computer secure without such knowledge is like trying to win the superbowl without knowing anything about your opposing team. Meanwhile, your rivals will definitely be working hard to learn everything that they can about you and your tech. So, you want to ‘win’ and keep your desktop, laptop, tablet, etc. secure? Then, you must first learn some of the core components of the game.

The Computer Virus

Man running, frustrated with computer problemsThe first malicious program you’re going to want to study and know like the back of your hand is the computer virus. Computer viruses are a lot like human viruses. They live off a host and spread to others by contact when the opportunity arises. The host in this case is an executable program or file, which means someone has to hit the download, run, execute, etc. option on the file in order for the infection to actually spread. Until then, it will sit quietly like a dormant volcano. If you allow it erupt, it may destroy any number of important programs, files, etc. on your machine. The home of these viruses may be an attachment in an email or other message where unsuspecting individuals are more likely to find, open and release them.

So, “Computer viruses are small software programs that are designed to spread from one computer to another and to interfere with operation by corrupting or deleting data, using your email program to spread itself to others, or even erasing everything on your hard disk.” (Microsoft)

The trick to avoiding that unpleasant scenario is to simply avoid opening emails from people you do not know or that are entirely unexpected, even if it seems to be a wonderful offer from a legitimate source. Remember, viruses wear very attractive disguises (e.g. images, greeting cards, audio, video, documents, other file types) for those that don’t know to look too closely. You can also find viruses disguised as seemingly normal download options on the Internet, which is why you should adequately research anything you’re planning to load onto your computer before doing so every time, all the time. If you’re not certain, simply do what you would for your own physical health: Seek a second opinion, preferably from a specialist.

Also, “To help avoid computer viruses, it's essential that you keep your computer current with the latest updates and antivirus tools, stay informed about recent threats, run your computer as a standard user (not as administrator) and that you follow a few basic rules when you surf the Internet, download files and open attachments.” (Microsoft)

  • Pro Tip: For some great email security tips you can check out a demonstration by Tim Bulu, Director of Information Security for USF Health Information Systems at

Computer Worms

Laptop infested with wormsThe second malicious program you should be aware of is the computer worm. Computer worms are programs, quite similar to viruses. In fact they’re a subclass of viruses but with some unfortunate advantages. Like the virus, worms love to spread their infection from computer to computer. However it does so by traveling through network connections, like the Internet (the most well known network), and then by making copies of itself on computers. To understand how this happens, consider one of their odd but interesting, origin stories:

“On November 2, 1988, a Cornell University student named Robert Morris released an experimental self-replicating program onto the internet to find out how many computers were currently connected to it. The program spread rapidly, installing itself on an estimated 10% of the computers then connected. Morris had no malicious intent, but a bug in his program caused many of the computers the worm landed on to crash. He was prosecuted and expelled from Cornell, but worms had come of age and have since evolved into an effective way of attacking systems connected to the internet. Most internet worms are now malicious." (BBC)

Once a worm is on your computer it doesn’t need to wait for you to unleash it because it’s basically network-aware and can do the damage on its own. Once it acts, it can take control of your machine in order to crash programs, steal data (e.g. identity, private information, etc.), make holes for further infections or even turn the computer into a zombie a.k.a. “bot” to be controlled remotely. Note that bots are gathered up by hackers, become botnets (i.e. groups of bots) and ultimately allow them to spread many more viruses, spam and to conduct other types of online fraud or crime.

So how can you keep your computer healthy and worm-free? You can start with a reputable anti-virus program. But because those aren’t enough all on their own for the highly adaptive computer worm, you’ll also need to use a firewall, which will act as a 24/7 watchman for your network traffic. In addition, you can use browsing best-practices, like surfing the web with restricted rights as a user rather than an administrator for your own security.

  • Pro Tip: Microsoft Security Essentials is one free and simple option that can help to guard your computer against viruses, spyware and other malicious software

Computer Trojans

Computer trojan horse illustrationLast but not least is the notorious computer trojan. Trojans are like con artists, in that they masquerade themselves as something they’re not so that they can attempt to gain your trust in order do their damage. Technically speaking, a trojan is a computer program that looks harmless but actually contains malicious code that will do harm once installed. The term, trojan “Comes from Greek mythology about the Trojan War, as told in the Aeneid by Virgil and mentioned in the Odyssey by Homer. According to legend, the Greeks presented the citizens of Troy with a large wooden horse in which they had secretly hidden their warriors. During the night, the warriors emerged from the wooden horse and overran the city.” (TechTarget)

One way to differentiate a trojan from a virus or it’s relative the computer worm is to remember that unlike the former two, trojans will not reproduce by infecting other files. Also, a trojan will never multiply to make copies of itself. However like the virus and worm, trojans can damage your files, create backdoors and generally do a lot of unnecessary damage to your system. Unfortunately, “According to a survey conducted by BitDefender, Trojan-type malware is on the rise, accounting for 83 percent of the global malware detected in the world.” (Wikipedia)

To avoid a stealthily disguised trojan you’ll need reputable antivirus software, which will prevent, detect and remove any malware, including trojan horses. Symantec Anti-Virus is one great resource for personal computers, today.

You can check out a quick video on this topic on YouTube!

A Quick Recap on Viruses, Worms & Trojans:

  • Viruses, worms and trojans are all malicious programs that can damage your computer
  • Viruses live and spread from programs and files but require human action to work
  • Worms will spread and multiply via networks and work without human action
  • Trojans hide in useful looking programs but wait for a human action to work

Keeping It Secure

Now that you know the differences between the virus, worm and trojan, let’s take a moment to review a few of the steps you need to take to avoid running into them on your device(s):

Step 1: Keep your operating system (OS) up-to-date at all times

Step 2: Use reputable anti-virus software and keep it updated for new threats

Step 3: Use a firewall that prevents unauthorized access to your device

Step 4: Research anything you’re downloading and do so with caution

Step 5: Never open unfamiliar or unexpected emails, messages or attachments

Step 6: Use strong passwords. “Passwords should be at least eight characters in length, comprised of alphanumeric characters and changed regularly”, according to The Journal

Step 7: Opt to have a professional run a simple disc scan, occasionally

If you remember to to follow this short set of rules and stay tuned into current Safe Computing standards with our team here at Health I.S., your risk of contracting a virus, worm or trojan will be significantly reduced. So share the good news with your friends, so that they can stay safe online and offline with a little bit of insight into how to keep their tech secure, too.

USF Health Information Systems is a comprehensive technology group serving the needs of the Academic Research and Clinical missions. We partner with our customers to deliver agile responsive technology solutions that drive business value and make life better for our students and patients. Be informed at all times by visiting You can connect directly via phone by calling (813) 974-6288 or by sending us an email via, after hours.


Bekah Witten
Visit this author's

USF Health


Bekah is the content writer for the University of South Florida department of Information Technology.