I'd recommend Norton Antivirus software as the most effective choice for preventing virus and malware infection. You can purchase an annual license for up to 5 computers from Amazon: Norton Security Deluxe 3.0 - 1 User, 5 Devices and Utilities 12 Month License Card (PC/Mac).
You will be sent a packaged license key with instructions for creating an account with Norton and installing the software on your devices.
Prevention really is better than cure!
Click the image below to purchase directly from Amazon.
Visit my Facebook page: www.facebook.com/DavidMorleyCS