Provided your computer uses Norton to protect its system from attacks, it is important that the software is kept up to date. Doing otherwise may leave it vulnerable to the latest attacks or prevent it from receiving other necessary updates. The Norton AntiVirus engine is common to the Norton AntiVirus, Norton Internet Security and Norton 360 products and requires frequent updates for ideal protection against spam, spyware, phishing and malware.

Installation

To begin the installation process you'll have to go to the Norton AntiVirus website, where there is a Virus Definitions & Security Updates section. There you'll find that definitions are downloaded by product and operating system. Norton requires a valid subscription for keeping its software up-to-date. Provided you need to update your subscription, you'll find a link to do so at the top of the page. Likewise, if you need all the security updates instead of just the definitions, those are available on the page as well. In the center of the page you will find a drop-down box labeled "Select Product." Subscription costs vary, according to length (one year or two) and product. There are all-in-one security systems, PC security software, PC tune-up software and Mac software for personal, multi-use and business systems. Norton AntiVirus, Norton Internet Security 2010 + Norton Utilities and Norton 360 are the most common. After ensuring your subscription is up-to-date, you will have to select the appropriate file name. The appropriate file name can be determined by matching the Symantec antivirus software you have installed to the products listed below the file names in red. Clicking it will bring up a file installation prompt, in which you'll have to select "run." Your computer will automatically install to the appropriate place once you do so, provided your software was loaded in the default file. If it was not, you will have to manually input the appropriate location. Space needed will vary, depending on the update. When the installation is complete, be sure to restart your computer, but only when prompted to do so.

Source:

Norton Virus Definitions & Security Updates