Most of us don't make a real difference between worm, virus and Trajan Horse or refer to a worm or Trajan Horse as a virus.

All of us know all are malicious programs that can cause very serious damage to PC. Exist differences among the three, and knowing those differences can help you to better protect your computer from their often damaging effects.

A computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Some viruses cause only mildly annoying effects while others can damage your hardware, software or files. Almost all viruses are attached to an executable file, which means the virus may exist on your computer but it cannot infect your computer unless you run or open the malicious program. A virus cannot be spread without a human action, (such as running an infected program) to keep it going. People continue the spread of a computer virus, mostly unknowingly, by sharing infecting files or sending e-mails with viruses as attachments in the e-mail.

A worm is a program or algorithm that replicates itself. A worm has the capability to travel without any help from a person from PC to PC and have ability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself, creating a huge devastating effect.

A Trojan Horse is a destructive program that "working" as a benign application ( (like changing your desktop, adding silly active desktop icons) or can cause serious damage by deleting files and destroying information on your system. Trojans are also known to create a back door on your computer that gives malicious users access to your system, possibly allowing confidential or personal information to be compromised. Trojans do not reproduce by infecting other files nor do they self-replicate.

Added into the mix, we also have what is called a blended threat. Blended threats combine the characteristics of viruses, worms, Trojan Horses, and malicious code with server and Internet vulnerabilities. By using multiple methods and techniques, blended threats can rapidly spread and cause widespread damage. Characteristics of blended threats include: causes harm, propagates by multiple methods, attacks from multiple points, and exploits vulnerabilities. This combination of method and techniques means blended threats can spread quickly and cause widespread damage. Characteristics of blended threats include: causes harm, propagates by multiple methods, attacks from multiple points and exploits vulnerabilities. They are considered to be the worst risk to security since the inception of viruses, as most blended threats require no human intervention to propagate.

Therefore is very important to protect your PC with a good anti-virus software installed on your system with the latest fixes for new viruses, worms, and Trojan horses.

Additionally, you want to make sure your anti-virus program has the ability to scan e-mail and files as they are downloaded from the Internet. This will help prevent malicious programs from even reaching your computer. You should also install a a system that prevents unauthorized use and access to your computer (firewall as well). 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.