My computer says my security is out of date; the last time I installed it was April of 06 and it was the one?

that came with at&t yahoo. What exactly do I need to do, and how? Please give a very detailed answer-thanks!
Please explain how to steps
the pop up says "your anti-virus protection may be out of date - what do I do to fix this - how to steps - thanks again
also what is the difference in anti spy and anti virus and how do you remove one and replace it with another?

What other security systems do I need to install on my COMPUTER in order to be fully protected?

I have downloaded Yahoo Anti-Spy.
Do I need to have other security systems installed such as Norton, McAfee, Webroot etc. in order to have my computor totally protected from hackers, I.D. theft etc.

How do you get a rogue security spyware popup off your computer?

This is a company that is trying to get me to buy their spyware. They are constantly warning me that my computer has viruses and other dangerous things on my computer and yet my Norton and Yahoo Anti-Spy says that I don’t

What computer security software do you use?

Do you use anti-virus software? And do you use it in combination with anti-spy/adware software? And what would you recommend? Are anti-hijacking apps also necessary?