For the question about NAV, once NAV learns about a virus, it will always detect it under normal circumstances. and since NAV even complains when a file tries to write to the registry and such, it does a realatively good job. on the other hand though, i have seen/participated in defeatin NAV with existing viruses. Under the proper circumstances, viruses can be "cloaked" (pardon the phrase, it just the best one i could think of at the moment) but there are ways to slip viruses by it, it's just difficult to get past the definitions, esp if they are up to date.