As far as I can tell, there is a disincentive to have a runner deck that concentrates too much on virus counters. The corp purges all virus counters for a fixed cost, though that cost is significant. However, the more the runner concentrates on getting virus counters, the move value the corp gets for that fixed cost. There doesn't seem to be enough synergy encouraging specializing in virus counters to justify it, is there?

That is, it seems you get the most effect for just having 1, maybe 2 virus counter-related tricks. After that, it's diminishing returns.

And, yes, the corp can still win, even when skipping one out of every 2 or 3 turns to purge virus counters. This is when the runner deck relies too much on virus counters such that it can't function without them and needs more than 3 turns to build back up again. Even worse when the runner spends resources and the corp only spends actions.

Is there much incentive to specialize rather than dabble? Anything other than the original Anarch identity card?

Of course there is. More viruses on the table means more virus counters piling up much faster which means the Corp, in order to respond to the threat, has to give up more and more whole turns, which is good for you! The more viruses you can stick on the table, the better.

Anarchs also benefit from Grimoire, Deja Vu, and Cyberfeeder, as well as the original identity card. None of those convey direct benefit from having virus counters present, but they significantly strengthen decks built around viruses - specifically, Anarchs get a much higher efficiency from virus cards than the other factions do.

Where virus counters can be used by you for your benefit - for example, on Crypsis - you're better off using those counters before the corp can purge them.

Yes, viruses work best with Noise, but they can be really mean when used right no matter what. Probably the best combo is with DejaVu, Aesop's and any purged virus card. With an empty, and useless virus card, trash it using Aesop's, then with the money made use DejaVu and still come out a credit ahead.

Gathar said:

Actually, no, you would break even, because you have to spend an action to play Deja Vu, which is the equivalent of spending a credit.

As some have pointed out, loading up on viruses can encourage the Corp to waste a turn, which is never a bad thing. HOWEVER, if you actually have it in mind to use the virus counters, then your best option is to just use them. That is, once you get your Datasuckers loaded, make use of them before the Corp's turn. Once you find an opening in R&D, run it several times in a row to maximize your Mediums. Once you install Imp, trash like crazy. Once Parasite get's built up to a certain critical point, finish off the ice with your Datasuckers or Wyrm. Playing a deck that depends upon viruses, or at least significantly uses them, really depends upon either finding the right balance for having the maximum number of virus counters in play that won't cause your opponent to want to purge them, or just exploding with them on a turn-by-turn basis.

My current Anarch build focuses on virus to mill the corp's R&D. I make use of their abilities/tokens when I can but they are secondary bonuses as the main purpose of the viruses in the deck is to force cards into the Archives. They also serve as fodder to Aesop's Pawnshop to make credits and keep the flow of viruses going. Other cards that help with this are Grimoire, Djinn, and Deja Vu. Crypsis is also great in the deck as he keeps the rig lean, can break any type of subroutine when you do need to run, and he also triggers the virus trash effect of Noise.

In short, if you are using the viruses for their effects and need their tokens, you need to manage them carefully and don't build up a lot to make it worth the corp doing a virus scan.