Someone generated a seed for the Mersenne Twister, with the intent of that seed producing this string:
Which is 20 characters long. Why he did it is explained below, but I don't know how he hacked it.
Why he did it:
The user feersum on Code Golf did this to generate a Hello, World! program in the Seed programming language. Obviously he didn't merely brute force his way to this seed, which is 4200 digits in length. How did he do this? Furthermore, this user has other answers in which he uses what is presumably the same trick, see: this answer.
What we know: The seeds tend to be quite large (much larger than if they were brute forced by addition-and-generation). Furthermore, every seed he finds must generate 624 integers with the seed before twisting the next 20 to produce the above string's numerical data. The complexity to brute force a string of n length is O(96^n), very complex indeed.
What I suspect: He filters what seeds he generates in such a way as to reduce the complexity for n length to about O(log(96^n)), which simplifies to O(1). I don't think that "he has access to a supercomputer" is a viable answer.
An acceptable answer: Anything which explains how he might have done this, even if he actually did it differently. It might take a long time for the answer to this to be known.
Interesting Mersenne Twister trivia: You can generate the state of the Mersenne twister with as little as 624 outputs, then predicting future output from it.
Note: Several bounties were pledged on the Hello, World! question for him if he were to explain how he did it. Years have passed, and he is not budging. Maybe those bounties will be passed on to you for having explained this.