Figure 3.

Effects of a larger-scale attack. The number of originally contaminated letters is N = 100 (instead of N = 6). The entries in the first columns of the contamination matrices C increase as p increases from 1 to 250, corresponding to an increased capacity to cross-contaminate. The number of contaminated letters (A) and the number of infections (B) increase linearly with p rather than as a higher power of p, because the mechanisms of cross-contamination are only affected by an increased capacity of the original letters to cross-contaminate, and not the subsequent generations.