This page contains spoilers about the Heartbound ARG. If you want to solve the puzzle yourself, avoid reading this article.
As this is the beginning of Phase 3, the first task is to actually find the trailhead. All we have to go on is a single word: "strings".
Strings is a well known Unix program to print out the legible character strings in a binary file. When we run
strings on the Heartbound binary, there's a very suspicious entry
It is more easily found by unpacking the provided executable. Then we find that
STRINGS.wav is a file, and the only .wav file in there.
Playing the .wav we hear a mix of a stringed instrument and the sound of someone dialing a phone. The latter tones are called DTMF and there are tools on the web to detect and decode them. Running the given tool on the file we get the following sequence:
3 444 2 555 33 3 444 66
(Note how sometimes the next tone begins almost immediately after the previous, and sometimes there's a full second of delay.) Anyone who sent text messages by phone before smartphones will recognize this instantly. It is Multi-tap.
It would be the work of less than a minute to decode it. We use dcode's Multi-tap Decoder to get "DIALEDIN".
Since this is Phase 3, and we're starting over (again), put that right in the URL right after "Heartbound/", and you'll get the What Have You Done page.