I use frostwire but Im afraid Im going to get a virus on my computer b/c my last computer crashed due to limewire, whats the best virus protection i could download that would protect my computer from viruses/spyware?

I just bought a new computer and now have windows 7. Any time I shut down the computer or reboot I am asked for my password. I do not want to put in my password everytime I reboot my computer. I didn’t have to do this with my last computer. What can I do so that my computer will not ask for a password and I can automatically come in?