First we will look into checking exisiting programs running in the background. These can bog down your computer, interfere with other programs you do want to run and just slow things down. Sometimes they can be tracked down to multiple icons in your system tray (your system tray is on the lower right of you screen.

Some icons in your system tray are beneficial, such as music players, firewalls or existing spyware and virus checkers. If you see a lot of icons, or notice some very new ones, it might be due to spyware.

These programs can direct you to advertising sites or record your Internet surfing activities to download even more advertising.

Symptoms include sluggish performance, a new home page or search engine for your Internet browser, or persistent modem activity even when you're not sitting at the computer. You can infect your computer just by visiting certain sites, having certain pop-up ads appear on your desktop, or from downloading free software. A number of programs are available that can diagnose and quarantine these pests.

Spybot Search and Destroy
It's free, without even an annual subscription for the periodic file updates (I check mine weekly). Spybot offers both basic and advanced modes and includes the widest variety of customization. You can schedule it for automatic updates (I do mine weekly). Spybot was thorough, rooting out even obscure spyware. As a first step, it can't hurt to download a free copy of Spybot to see whether your system is infected.

Get a Second (or Third) Opinion
I run another program, also free, called Ad-aware SE Personal Edition. I find it very thorough.

Also free is Microsoft AntiSpyware (currently beta), which includes automatic updates and scheduling options.

Given that no single antispyware app can find and quarantine every piece of spyware, we recommend you run all three free apps; that way you're sure to get rid of as much spyware as you can.

If you make an effort in prevention by using these tools and keeping them updated, you should run into few problems and keep your computer running quicker and with fewer annoyances.