❏This vs That ❐: Virus vs Worm vs Trojan

I know you've all heard of them at one time or another - or even worse - experienced them.  The term "computer virus" is sometimes used as a catch-all phrase to include all types of malware, even those that do not have the reproductive ability. Malware includes computer viruses, computer worms, Trojan horses, etc.  Viruses are sometimes confused with worms and Trojan horses, but there are differences among the three:


Computer Viruses
A computer virus is a small program written to alter the way a computer operates, without the permission or knowledge of the user. A virus must meet two criteria:

• It must execute itself. It often places its own code in the path of execution of another program.
• It must replicate itself. For example, it may replace other executable files with a copy of the virus infected file. Viruses can infect desktop computers and network servers alike.

Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are not designed to do any damage, but simply to replicate themselves and make their presence known by presenting text, video, and audio messages. Even these benign viruses can create problems for the computer user. They typically take up computer memory used by legitimate programs. As a result, they often cause erratic behavior and can result in system crashes. In addition, many viruses are bug-ridden, and these bugs may lead to system crashes and data loss.


Computer Worms
Worms are programs that replicate themselves from system to system without the use of a host file. This is in contrast to viruses, which requires the spreading of an infected host file. Worms spread from computer to computer, but unlike a virus, it has the capability to travel without any human action. A worm takes advantage of file or information transport features on your system, which is what allows it to travel unaided.  Although worms generally exist inside of other files, often Word or Excel documents, there is a difference between how worms and viruses use the host file. Usually the worm will release a document that already has the "worm" macro inside the document. The entire document will travel from computer to computer, so the entire document should be considered the worm.   W32.Mydoom.AX@mm is an example of a worm.


Computer Trojan Horses
Trojan horses are impostors—files that claim to be something desirable but, in fact, are malicious. A very important distinction between Trojan horse programs and true viruses is that they do not reproduce by infecting other files nor do they replicate themselves. Trojan horses contain malicious code that when triggered cause loss, or even theft, of data. For a Trojan horse to spread, you must invite these programs onto your computers; for example, by opening an email attachment or downloading and running a file from the Internet. Trojans are also known to create a backdoor, (an undocumented way of gaining access to a program, online service or an entire computer system) on your computer that gives malicious users access to your system, possibly allowing confidential or personal information to be compromised.

Tips to Combat Viruses, Worms and Trojan Horses on Your Computer

Keep The Operating System Updated

The first step in protecting your computer from any malicious there is to ensure that your operating system (OS) is up-to-date. This is essential if you are running a Microsoft Windows OS. Secondly, you need to have anti-virus software installed on your system and ensure you download updates frequently to ensure your software has the latest fixes for new viruses, worms, and Trojan horses. Additionally, you want to make sure your anti-virus program has the capability to scan e-mail and files as they are downloaded from the Internet, and you also need to run full disk scans periodically. This will help prevent malicious programs from even reaching your computer.

Use a Firewall

You should also install a firewall. A firewall is a system that prevents unauthorized use and access to your computer. A firewall can be either hardware or software. Hardware firewalls provide a strong degree of protection from most forms of attack coming from the outside world and can be purchased as a stand-alone product or in broadband routers. Unfortunately, when battling viruses, worms and Trojans, a hardware firewall may be less effective than a software firewall, as it could possibly ignore embedded worms in out going e-mails and see this as regular network traffic.

For individual home users, the most popular firewall choice is a software firewall. A good software firewall will protect your computer from outside attempts to control or gain access your computer, and usually provides additional protection against the most common Trojan programs or e-mail worms. The downside to software firewalls is that they will only protect the computer they are installed on, not a network.

It is important to remember that on its own a firewall is not going to rid you of your computer virus problems, but when used in conjunction with regular operating system updates and a good anti-virus scanning software, it will add some extra security and protection for your computer or network.



Conclusion
In a nutshell, a Worm will attack your computer by itself, whereas a Virus requires you to install it by downloading it from the network or storage device. A Trojan Horse is a malicious program that presents itself in an interesting or entertaining manner (e.g a free game, beautiful screen saver, mp3 song etc), but it harms the computer.





Resource(s):  symantec.com, webopedia.com, wikipedia