If your computer is connected to the Internet, chances are that some Web sites you have visited have attempted to install programs on your computer that you don't want. There are now hundreds, perhaps thousands, of these programs, often referred to as “adware” and “spyware.” These programs can also come along for the ride when you download other programs, or they can get installed on your computer when you innocently click on certain Web links.

Without your knowledge, these programs can track your Web activity and send the data to an advertising company, take over your browser and change its home page, add “options” to your browser's toolbar, change the way your computer operates, slow your computer down, put advertising on your screen, and pull many other undesirable tricks. (See for more gory details.)

Unfortunately, conventional virus detection programs, important as they are, do not detect these programs. So in addition to an updated virus checker running all the time, you should also periodically scan your system for adware and spyware. Fortunately there are at least two very capable and highly recommended free programs (for PC only) that can do this for you. I suggest that you use both of these programs regularly; each of them can detect some unwanted programs that the other might miss. Ad-aware, by a company named Lavasoft, can be downloaded from . Version 6 was the current version at the time of this writing.

Spybot Search and Destroy by PepiMK Software is found at .

Each of these programs uses reference files that need to be updated as new problematic programs appear on the Internet. Keep your spyware detectors up to date just as you do your virus checker.

“TechNotes” runs in each issue of TAP, with the aim of educating us about aspects of technology and communications relevant to our work.