Some freeware programs you might install on your computer are ‘bundled’ with spyware programs. File-sharing programs like iMesh and Kazaa are notorious for this.
Sometimes, sites (or pop-up ads) try to fool you into clicking ‘Yes’ by stating that the advertised software is required to view a particular site. You may also experience numerous “error” windows if you click ‘No’ on a particular ad. Rather than click on an unknown ad, you should click the “X” in the far right-hand corner of the window to close down unwanted ads or pop-up windows.
Note: You should never click ‘Yes’ to a “Do you wish to download and install…” prompt unless you are 100% positive that you trust the publisher of the software. Read the dialogue box very carefully before clicking on the ‘Yes’ button.
You can also do your best to guard against spyware by ensuring you have the latest updates and patches for your version of Internet Explorer. These are available from Microsoft at support.microsoft.com