I actually thought this might get posted to HN, so I went through a lot of pain to find back a way to get my HN login back (basically had no access to the email with which I opened an account here: I had to dive deep down in some Google Suite tied to a domain name to find a way into the user account and eventually reset my HN password). I'm glad I did in time and didn't miss this thread!
> Was this a side project? did it require much attention after the initial setup?
Totally a side project.
It hardly required any attention: just making sure the computation was running and making sure to backup the intermediate results once in a while (I had backups everywhere of the intermediate results: remote servers, USB keys, DVD, other computers at home, email, etc.).
I only needed to do a few tiny steps once I found the secret message (which contains a number which allows to compute one of the two prime numbers).
> Did you knew for certain that your program will solve the puzzle at some time?
The description of the problem itself explains a way to verify that intermediate results are correct.
> Did you have an estimation of the date?
Yes and that one is easy: I wrote a little piece of code (in Clojure, whatever, it's unrelated to finding the solution) which would check at which intermediate result the computation was and then compute an "ETA".
Fun story: I'd regularly send my brother something like this...
