I facecheck some unrezzed ice and run into a rototurret and I cant break the sub. The corp chooses to destroy my datasucker with 6 counters on it. Am I able to use any of those counters in response before I destroy it?

Datasucker says "...rezzed piece of ice currently being encountered..." so the only thing you can do is lower rototurrets strength from 0 to 0 and you can spend all 6 virus tokens on it if you want but that's about it.

True. Thank you.

No problem. Also technically, timing-wise you can only spend your datasucker tokens before the subroutine goes off. Once the subroutine goes off the only activated abilities you can use are "prevent" type of abilities.

Yeah, it's less useful against roto because it's already strength 0, but if you ran into a Grim which already had a parasite on, you could use Datasucker to bring it to 0 and trash it before the subroutine could ever fire.

Is there a ruling somewhere that says you do not reduce its strength to -6?

I can't see a point, but I did think the strength could be negative.

V.

Well you could make it Strength -6, but as you say what would the point be? You're spending Datasucker tokens for no benefit.

The Strength of ICE can indeed be lower than 0, as the wording on Parasite implies. It's also relevant for Atman (as a Str 0 Atman couldn't break a Str -1 ICE, so you could actually hurt your own game by using Ice Carver).