When you pick a winner for your campaign we include all qualified entries (including any bonus entries) in the pool of entries for a random winner to be selected from.
We then use the Mersenne Twister, which is a random number generator (to be specific, a deterministic random bit generator), to select a winner. It is called the Mersenne Twister because its period length is chosen to be a Mersenne prime.
How the Mersenne Twister works
Why we use the Mersenne Twister method
This method passes numerous tests for statistical randomness, including the Diehard tests and most of the TestU01 tests.
This method has an extremely long period of 2^19937 − 1. While a long period is not a guarantee of quality in a random number generator, short periods, such as the 2^32 common in many older software packages, can be problematic.
It is k-distributed to 32-bit accuracy for every 1 ≤ k ≤ 623.
This method generally creates random numbers faster than true random methods. A study found that the Mersenne Twister creates 64-bit floating-point random numbers approximately twenty times faster than the hardware-implemented, processor-based RDRAND instruction set.
This method is permissively-licensed and patent-free, which allows us to use it for POPSMASH at no charge.
The result is that you can be confident that with any campaign where the winner is selected randomly by POPSMASH, the winner was chosen in a secure, truly random way with no undue influence.