Years have passed since the age of innocence in the computing world. Nowadays, there exists an increasing variety of malicious software programs as well as e-mail messages carrying them. Most of these programs can either be classified as viruses, worms, spyware and trojans. Amazingly, one of the victims of such programs was Ed Gibson, Head of Security for Microsoft UK, whose PC was infected by a dialer and started transmitting such programs to other unsuspecting victims.

Before we start, however, here are some quick definitions:

Worms, Viruses: Malicious executable code that can copy itself from one PC to another. Most of them don't perform any other operations apart from simply copying themselves. They can, however, multiply like that very quickly and clog a system. The famous Internet Worm actually brought the whole Internet on it's knees, back in 1988.

Trojans: Seemingly harmless programs but not really. They can be disguised as utilities, or as a system process but actually contain executable code intended for other tasks. A trojan may contain a virus, or a backdoor through which an intruder can have complete access to your PC.

Spyware, adware: Programs that spy on your PC and record and transmit data such as the sites you usually go to, the fields in on-line forms you use (such as your e-mail accounts, your credit card numbers and generally everything you enter in a web form). They are usually VERY poorly written programs and as such, will often slow down your PC or corrupt your software. (Yes, if they were really good written, they would actually go by unnoticed. Lucky for us, most talented programmers have jobs writing real software rather than parasites...)

Dialers: Programs that use your modem to dial numbers without you being aware of them. With the use of broadband connections, they tend to become a thing of the past. And we'll not deal with them in this article.

It is worth mentioning that in recent years, a significant increase in the number of adware and spyware programs has been noticed, with a subsequent reduction in the number of new viruses being created. This can be explained as follows: While viruses can be a serious threat and can greatly and irreversibly harm your system, adware and spyware programs can actually gather very important personal information such as your credit card number and deliver that information to whoever was responsible for the attack, which most of the times is the creator of the program. An effective system security tool should not just locate these malicious files on your PC but should also be able to permanently erase them.

Most anti-virus programs can successfuly locate, identify and remove viruses but things are not as easy when it comes to spyware and adware. There is no product in the market that can eliminate 100% of spyware. It is therefore recommended that you install and periodically run at least two anti-spyware programs. It would be better if at least one of your chosen anti-spyware programs offers some kind of real-time protection. This means that a component of the anti-spyware programs stays resident on your computer memory and monitors traffic between your PC and the Internet. If a web page tries to send malicious code to you, or if an executable file tries to install that code, the anti-spyware resident component will detect it and block it. You can then, periodically run another anti-spyware program to scan your disk, in case something was missed by the first program (as we've said, no program currently detects and removes 100% of spyware).

Finally, it is crucial to frequently update your anti-spyware program or programs. New spyware programs are created all the time and it might be often that you find your PC infected with the latest spyware that your anti-spyware program failed to detect before you updated it. So don't forget to update your anti-spyware about once a month to be as safe as possible!