This is an extremely powerful card, but one that doesn't really do much on its own.
To exploit Hivemind's ability, you should use those viruses that won't consume the virus counters on it. The following is a list of those that will benefit the most from this card's presence:
- Chakana becomes a very good fast advance counter;
- Darwin, which usually suffers a lot from purges, won't fear 'em anymore;
- Deep Thought... well, admittedly this one isn't such a good card;
- Gorman Drip v1 can make you gain money with no counters on it, and you'll feel like cheating;
- Medium to go deep down the R&D's hole;
- Nerve Agent if what you search is not in R&D;
- Parasite becomes an instantaneous ice killer;
- Pheromones can have some recurring credits with no effort;
Now, Hivemind comes with one virus counter on it, free of charge, but you need a way to keep at least that single one on it, because this card does not offer a way to gain more of them. You just need a Progenitor to host it, and it will be somewhat safe from a purge.
Incubator, on the other hand, is your main source of virus counters, and once you have a few, you'll be able to do insane stuff. Let's say you have 5 virus counters on Incubator: you trash it to move all of them on Hivemind, which now will have 6. Suddenly, your Medium (which was void of any counters) is worth 6 extra cards from R&D (keep in mind you'll add another virus counter before accessing). Your Parasites will kill any piece of ice with strength 6 or lower on install.
If that's not enough, keep in mind that all the virus counters on Hivemind will are considered hosted on all other virus programs. Why is that important? Well, just imagine installing another Medium... voilà: accessing to 12 extra cards from R&D. How about that?
Not enough to satisfy your need for wanton destruction?
Well then, why don't you make a Demolition Run instead.
Of course, you could always use the counters on Hivemind with other viruses, that will consume them... like Gravedigger, for example. Yes, this Hivemind will let you do some crazy stuff, just take a look at this awesome deck: Can o' Whupass... even if just for the description!