Here is my example:
Runner has a Parasite with two virus counters installed on a six strenght Ice (archer for example) and a Datasucker with four virus counters so ha decides to run on the Archer. The corp then rezzes a Corporate Troubleshooter to raise the strenght of the ice.
How are the paid abilities on Datasucker and Corporate Troubleshooter then rseolved? Can you pay two virus counters from Datasucker, see what the corp does and then use the two remaining?