So you, like most people, have probably had your computer get infected with viruses, spyware, and other malicious software. If you have brought your computer somewhere to have these viruses removed I'm sure you have been charged a lot of money, probably had a lot of security software pushed on you, and probably been given a headache with the process in general of dealing with whoever is fixing your computer. Here are a few steps that can help you prevent these problems on your computer as well as fix them yourself if they do appear.
For prevention of these problems i would recommend installing microsoft updates whenever they are available. Your computer should do this automatically, but if you receive any notifications that updates are availble for your computer you can go to update.microsoft.com to have your computer check to see what updates are available. Install anything that microsft update finds as most of these are security updates that close any vulnerabilities that your PC may have.
As far as virus protection, i would actually suggest the simplest form of whatever software you choose to go with. Personally, I recommend Norton Antivirus, but whatever you choose, do not purchase any of te security suites, or total protection packages. Just purchase the antivirus software. All of the personal firewalls, parental controls, and whatever else may be bundles with these security suites is unnecessary. Windows already has a built in firewall that works just fine. All these other features just add overhead to your PC, eventually slowing it down more than the things it is protecting you against would. Your antivirus software will come with 1 year of updates, after which you will begin receiving notifications that your subscription is expired and that you should renew online. I would not recommend this, instead go out and buy the new version of the antivirus software and install that instead. Why buy a new subscription to ANYantivirus 2010 when a 2011 version is out now.
A current antivirus program and keeping your computer up to date should be all the preventitive measures a home user should take, however for many people it is inevitable that your computer will become infected with some sort of spyware.
There is a free tool called Malwarebytes Anti-Malware that as of right now i feel is the best and only program you need to clean your PC of any type of infection. It is free and can be downloaded from the internet, just make sure the name is Malwarebyte's Anti-Malware, and not something similar. Download and install the program, and at the end of the install be sure to leave the box that says "update now" checked. This will cause the program to update itself before it is run for the first time. If you are not running this for the first time you can and should manually update it by clicking the update tab in the program and clicking the "update" button. Do this over and over until you it tells you you are on the most current version. Then click the "Scanner" tab and select the button to perform a full scan. Click "scan now" and make sure all of your hard drives are checked. If you are unsure what this means then just leave it as is. Click "scan" and the program will go through your computer and find any malicious software that may be running in the background. The scan can take anywhere from 15-60 minutes to complete. Once it is done a box will appear telling you to click "show results" to view what was found. Click this to show a list of malicious software found in your computer and then click "remove selected" to remove all items found from your computer. A box will most likely appear telling you that your computer needs to be restarted to complete the removal process. Click OK and your computer will restart.