Here is some explaination on guess_my_password.exe on KPMG Security Challenge 2016.

 so its PE64

looks like base64 string try decode it, i get nothing, so lets dive to the code again

 after some time i found it is a custom base64 with alphabet

0123456789qazwsxedcrfvtgbyhnujmikolpPOLIKUJMYHNTGBRFVEDCWSXQAZ+/

I found this website HERE
and paste the custom alphabet and decode the sting back and you get the flag
KPMG{th!5_is_to0_5impL3_RE}