Many viruses for Microsoft Windows can be prevented if you keep your operating system up to date. You may think it's a hastle to install Windows Updates, but it can save you a lot more hastle later. At very least, get the Critical Updates from the Windows Updates site.
Visit the Microsoft Windows Update Site after you have removed all the viruses and worms that you know you have.
Pop-ups and Ads
Mozilla Firefox users
Firefox comes with an pop-up blocker built in but some flash-based popups still get past it for which I recommend the extensions Flashblock and adblock.
Flashblock - Makes flash files require click before playing
Adblock - Blocks specified ads
Internet Explorer users
When it comes right down to it I recommend you get Mozilla Firefox.
Otherwise, Windows XP Service Pack 2 gives Internet Explorer a useful pop-up blocker. I also recommend the Google toolbar. It is clean and useful.
Only use these free virus scanners if you do not already have a virus scanner such as Norton Anti-Virus or McAfee Anti-Virus installed.
Here are two free online virus scans, all you have to do is go to one of these sites and it will scan your system and fix any viruses that it can:
Trend Micro HouseCall
Here are a couple of free virus scanners to install on your system to prevent later infections, or to get rid of what you have now:
AVG Virus Scanner
Adware and Spyware
Chances are, you have adware or spyware running on your system right now and you don't know it. It is a good idea to get one of these programs even if you don't think you are being affected by spyware.
Here are some free adware/spyware scanners that will scan your system and remove it:
Spybot Search & Destroy
It is generally a good idea to keep your registry from getting to large. This happens when applications are installed and then removed and registry entries get left behind that do nothing. This program is excellent for cleaning up your registry. Regcleaner is a great app for cleaning up your registry and for manually removing unwanted startup programs.