How do I avoid getting viruses
Always keep your virus definitions up to date.
What is difference between a virus and spyware
A virus is a piece of malicious software code written to damage your computer system. Where as spyware try to steal information from your computer and send that information back to it's owner.
Why is my computer so slow
There are several reason why your computer could be running slowly. It could be that you are running low on memory or you have some viruses on your computer