NAV is the biggest piece of S|-|!T in the AV history!!!
i strongly recommend you to use KAV. i did a test at work. in one pc i installed the latest versions of NAV and KAV. then i infected that pc with 10 new viruses (i'm a tech, so i get access to those things, i dont make them.. hehe).
THE RESULTS:
NAV: 2 viruses detected... boooooo
KAV: all 10 of them!!! whohooooo
KAV link:
http://www.kaspersky.com
they update their database every day, 4 times. there is an option that you can do the same, sync with their server.