There's basic & pro. Always get Basic to see how you go. There's only minor differences between the 2 & they are internal engine differences.

Norton doesn't always pick all viruses up. Personally I use AVG free. Audio files themselves don't have viruses. However formats such as WMA should be stayed away from. To learn more about these issues see (1) WARNING: Viruses on network you should be aware of! (click on link), & (2) What you should know about WMA/WMV Files

Basically stay away from files less than 2,000 KB (2 MB) in size. Some files get spammed that may have the same title as you're looking for but are spam or viruses, but these are generally below 2 MB in size. So filter your search results by audio initially.