About definition updates

Symantec provides updates for the following types of definitions:
Antivirus
Definition files contain the necessary information to detect and eliminate risks, such as viruses and adware. Symantec supplies updated definition files every day and whenever a new risk is discovered.
Symantec Protection Engine automatically uses the most current definition files for scanning.
URL
Symantec periodically supplies updated URL definition files. If you subscribe to content updates, Symantec Protection Engine automatically downloads updated URL definitions through LiveUpdate. Symantec might create new URL categories to address emerging URLs as needed. If you subscribe to the content updates, any new categories are automatically downloaded with the regular updates to the existing categories.
Symantec Protection Engine automatically uses the most current definition files for scanning. However, if a problem is discovered with the current URL definitions, you can revert to the previous set of URL definitions.
You must update Antivirus and URL definitions using LiveUpdate. When you perform a content update, Symantec Protection Engine downloads and installs the most current definitions. You must have a valid license to update definitions.
If an error occurs, Symantec Protection Engine tries to roll back to the previous definitions. If the rollback is successful, Symantec Protection Engine continues scanning using the previous definitions. If the rollback is unsuccessful, scanning is disabled.