1. The first function that most anti-spyware software packages offer is a feature to scan your computer's entire hard-disk (which includes both files on the hard-disk, and entries in the Windows registry - which is the place where configuration settings for your computer are stored) for spyware.

Older and less sophisticated anti-spyware packages typically looked for exact file names and highly specific registry entries, in order to detect spyware. Unfortunately, this approach means that spyware authors were able to avoid detection by simply changing file names or registry data either between versions or randomly in during each installation.

Today, most spyware packages use a considerably more sophisticated approach. They use a set of heuristics (rules) and look for signatures (specific sequences of data) to determine whether a computer is infected with spyware. This technique makes it very much harder for spyware to avoid detection, especially when these heuristics and signatures are regularly updated by the anti-spyware authors. However, there is one downside to this approach: very occassionally a totally innocuous file or application may be flagged as containing spyware in what is known as a "false positive". If you suspect a false positive, it is best to contact both the author of the application and the anti-spyware developer to verify it is indeed a false positive, and to get the problem rectified.

2. The second function that anti-spyware packages offer is the ability to remove spyware from your computer. It is necessary that this function is built-in to the anti-spyware package because many spyware programs actively resist being deleted, and thus manual removal is not possible.

3. The third function that anti-spyware packages offer is protection against new infections. This is one of the areas of greatest differentation between the various anti-spyware packages, so is one of the key areas that you should review when deciding which anti-spyware package to buy.

4. The fourth and final function of anti-spyware packages is one that I have alluded to throughout this article: the ability to update themselves in order to help protect your computer from new and emerging threats. This is an absolutely crucial feature as new types of spyware are found "in the wild" every single day.

All the leading anti-spyware packages have features that encompass each of the above areas, although they of course differ in detail as well as emphasizing different features. If you go with any of the leading anti-spyware packages, your computer will be much safer from spyware threats, and you will gain the peace of mind that comes from that.