There are many things that can slow a computer down, but nothing does more to negatively impact the performance of a computer more than spyware. Even many viruses run undetected, but almost all spyware prevents a system from running at top speed.
Spyware comes from a variety of places, but there are three types of web browsing that will guarantee that you accumulate some of the worst forms of spyware.
Online gambling sites: Not all online gambling sites are sources of spyware, but most of them are.
Online surveys and drawings via popups and spams: Many legitimate companies ask for your opinion through surveys, but surveys can also be lures for spyware. If you get a popup or spam offering a free iPod, laptop, ringtone, etc., consider it a trick to get you to download spyware.
Porn sites: Nothing will gum up your computer more than surfing for porn. Rick and I have laughed as we relate stories about clients with porn surfing habits. We will do total reformats or spyware and virus cleanups costing over $100 only to have our clients call us back a few days later with all of the same problems.
If you don't want spyware and a slow system, don't surf for porn, don't gamble online, and don't get intrigued by offers that seem too good to be true.
If you find this too difficult, be ready to pay for expensive cleanups every few weeks.
