Runner Dirtbags and Corporate Scum,

A question: when making a run on a server, is a runner permitted to continue spending credits to strengthen a program after a subsequent ice has been rezzed? Example: making a run on a server with Crypsis.First ice is rezzed Matrix Analyzer, strength of three.One credit is spent to beat trace subroutine, three credits are spent to increase strength of Crypsis to three. Matrix Analyzer is defeated, next ice is rezzed by corp. It's a Tollbooth, strenght five. At this point, if the runner opts not to jack out, is he stuck with a Crypsis with a strength of three, or can he pay the two credits to increase the Crypsis to a strength that will beat Tollbooth? Or, is each ice encounter a separate event requiring the runner to re-up a program as necessary for each encounter? Also, do program strengths in a runner's rig stack? 

Thanks in advance!

Boosts to icebreaker strength are only maintained for the encounter with that ice. So Crypsis would reset back to a strength of 0.

Unless, of course, the card says otherwise which is the case with the Shaper icebreakers. They explicitly say the icebreaker strength boost lasts for the duration of the run.

 Also, you only NEED to boost the strength of an icebreaker IF you want to break any subroutines on a piece of ICE. If a piece of ICE has one subroutine [Subroutine] Trace ² - if successful, give the Runner 1 tag, then you don't have to raise your icebreaker's strength at all if you just want to pay to beat the trace. Unless a piece of ICE has a subroutine of [Subroutine] End the run, you don't get stopped by it, you only get hit with the subroutines and then pass to the next ICE or to the server. In other words, in your example, if you pay one credit to cause the trace to fail, you don't need to raise Crypsis's strength at all, you just move on to the next piece of ICE.

 And program strengths do NOT stack.

 Thanks for the helpful replies! Another question in the vein of stacking programs. So, program strengh does not stack. That makes sense. What muddies the waters a little bit is when the rules say that multiple programs can be used in a single ice encounter, but is seldom useful. Seldom is not never, so when WOULD that action be useful, and how does it work?

Thanks again for answering my questions!

Best example I could think of would be using Wyrm to lower the strength of an ICE so that you can use Yog.0 or Mimic to break the subroutines (since they don't have any way to raise their own strength).