(rough notes that need expanding)
Can be made using either block encyption or hash algorithims. Either way, the seed needs to be random and unique. the uniqueness can be date time and fixed user info. Date-time guarantees uniqueness for the period of time before the number of bits used overflows. For example if 32 bits are used for the number of seconds since an arbitray, but unchanging date, then seeds every second will be unique for over 8000 years. User info guarantees that if another person , or computer if equiped with hardware true random, makes a seed at the exact same second; the PRNG output will be different. The probability of the true random bits being the same at different locations, or more than once at a single location is minscule, but not zero.