Fortuna is a cryptographically secure pseudorandom number generator (CS-PRNG) devised by Bruce Schneier and Niels Ferguson and published in 2003.
[2] Fortuna is a family of secure PRNGs; its design leaves some choices open to implementors.
Running out of pools would then take about 13 years, which Ferguson and Schneier deem long enough for practical purposes.
More paranoid implementors, or ones requiring the generation of random data at a colossal rate and correspondingly frequent reseeding, could use a larger number of pools.
Fortuna differs from the earlier Yarrow algorithm family of Schneier, Kelsey and Ferguson mostly in its handling of the entropy accumulator.