Whether you run anti-virus and anti-spyware or not, your computer can still be infected. This is due to the ever evolving nature of the internet allowing new innovations for good and bad. Now that your computer is infected, what can you do?
There are a few things you can do. One of them would be to format your had drive. This is the most time consuming and costly method. You will lose all your files and it will take you a very long time to re-install all your programs. This path should only be taken if there is no other course of action available, and if there is a deep infection.
If the infection is less severe there are some things you can do. You can clean your hard drive with anti-virus and anti-spyware software. There are many free programs out there that will do the job.
Once you have these programs you need to run a scan to determine where the infection is. Once the infection is located there are one of two things you can do. You can either quarantine the infection, or you can delete it completely. Deleting it would be the more effective option as it ensures you do not accidently use the file again. An important part of running these programs is keeping them upto-date. They need to be regularly updated to be able to combat the new viruses and spyware that pop-up on a daily basis.
A boot-time scan is recommended as a good course of action to remove your infection. Should you continue to experience slower PC speeds, you could try using a virus scanner to not scan only your hard drive, but prevent your PC from getting more spyware. Usually with spyware, once you have even a few files infected, they spread like a virus and attempt to propagate themselves. It's important that you have a virus scanner to not only delete old spyware, but prevent new spyware from popping up. Avast is great for this.
Keeping your computer 100% free from viruses and spy-ware is difficult but following the procedures above you can continue to enjoy the use of your computer.