What are some good free virus protectors?

[Enoch]

issue encountered: Lately my computer has been running slower...
possible resolution: Add more computer memory

issue encountered: pop-ups are coming on
possible resolution: keep most-frequent-use programs (hint: system tray); uninstall them

issue encountered: Today my yahoo account and facebook were hacked in the same hour...
possible resolution: gain access one at a time, e.g. open one web browser for each service. Please note that this is done if you don't want to add extra RAM to the computer. Make sure your web browser indicated a 'Lock' symbol in the URL, something 'Secure' or 'https://...'

issue encountered: I figure if I can get some good virus protector...
possible resolution: any anti-virus program that provide all-the-round clock real time protection, and set the quick scan scheduled task at 2 a.m. or when your computer is idle, weekly preferably.