Symantec provides different "tiers" of definitions depending on the urgency and the specific protection layer:
The virus definitions are regularly updated by Symantec to stay current with the latest threats. This is typically done through an internet connection, where the software downloads and installs the latest updates. The updates can include new virus signatures, improved detection algorithms, and other enhancements to help protect the computer from various types of malware.
To ensure optimal protection, follow these best practices:
Here’s a helpful, clear explanation of (often called virus defs or dat files ):