How is the seed of PRNGs generated? They can't be hardcoded I am guessing.
Absolutely not acceptable to "hard-wire".
A PRNG must have a purely random seed. Ideally that seed should come from non-repeatable physical sources and have uniform distribution with independent symbols.
The seed is the only random part of a PRNG, the rest is purely deterministic.
More on the definition below:
This may present some practical difficulties, one solution may be to pool a number of randomness sources as described below: