Newegg has Webroot A/V on sale for $7.99 after promo code EMCEGFF43 . One of the most lightweight and non-intrusive A/V solutions on the market.

http://www.newegg.com/Product/Pro...6832296101

Limit of 5 - The 1 year starts on activation date NOT from date of purchase - so you can buy multiple licences and be stocked up for years.