Many different types of malware and malicious code that negatively affect computers are referred to as simply "viruses", and there are several other terms you may have heard used to describe these harmful threats. The term "viruses" may be a bit self-explanatory, and is a result of the way that computer viruses infect host computers and then spread to others, similar to the way real-life viruses affect humans and animals. However, the origin of other terms for different types of malware, are not always as clear.
Computer worms are harmful programs with the uncanny ability to multiply on their own and spread like wildfire. The term "worm" used in reference to these types of malicious programs was first coined in the 1975 science fiction novel "The Shockwave Rider", by John Brunner, due to the way that it replicates and spreads out, infecting other hosts. Dangerous worms in real life are known to reproduce themselves and travel from host to host (both human and animal), causing various different types of damage.
Anyone with knowledge of Greek mythology can probably deduce the meaning behind the Trojan virus. According to Greek mythology, the Trojan horse was a giant wooden horse filled with soldiers used to infiltrate the city of Troy and launch a surprise assault. Similarly, the Trojan horse virus disguises itself as a non-threatening program to gain access and attack systems that download and install it. Trojan horse viruses may also come bundled with legitimate software, causing it to be installed along with the other application.
Due to the ever evolving sophistication of harmful malwares, the lines are now beginning to blur between worms and Trojan horses. Many new types of Trojan viruses are becoming more advanced and capable of spreading themselves similar to the way the worms operate. Since, by definition, a worm is a harmful application capable of reproducing itself, it is now becoming difficult to determine at what point a worm stops being simply a worm and should be labeled as something else.
Analyzing the ever growing and evolving lists of computer viruses can be daunting for the average computer user. Fortunately, most quality antivirus software is now equipped with searchable encyclopedias where users can pinpoint specific malwares and learn about their causes, effects, and the steps necessary to remove them from their system. Such lists are in need of constant updating, due to the fact that new viruses and other types of malware are springing up all the time. It is estimated that about 100 new types of malware are released into the online environment every single day (36,500 per year, with no end in sight).
If you believe that your computer may be infected with some type of malware, it is highly recommended that you run a virus scan to most effectively locate and assess the problem. If, despite your best efforts, you are still left with virus symptoms but no confirmed problem, it may be helpful to simply do an online search of the keywords relating to the symptoms that you are experiencing. Often times you may find articles or discussion groups with information pertaining to your specific problem, and many times you'll find helpful clues as to what is causing the abnormal activity on your computer. Once you've determined the type of virus, you can then systematically begin to research how to rid your system of it.
No matter what the name of the malicious code that you may be unfortunate enough to encounter, all viruses are dangerous to a certain degree, and should be dealt with as quickly as possible, not allowing them type to multiply or spread to other machines either via your network or via the internet.
