I love the STFs and seeing assimilated starfleet officers lumbering around is quite a sinister sight. However I take exception to some of the wording used in the STF missions.
Firstly, one is not 'infected' by the Borg, one is 'assimilated'. Secondly, its not a nanovirus, but nano probes!
Its just a small thing, and I accept that you can't really change the name of the mission 'Infected' now, but it just makes me a little sad each time I see this. Just a little change of wording in some of the mission dialog would be awesome!
Nanovirus is (reference: Unimatrix Zero), though it wasn't used in the same context.
Anyway, if you read the text in the normal Borg missions, it's actually covered somewhat. The Borg have started using a new, efficient method of assimilation that indiscriminately assimilates everything on an entire planet, not just the technology and sentient beings the Borg are actually interested in. Sounds a bit like the airborn assimilation system they had in Armada II.