WHOIS is usually useful in these cases:
$ whois projecteuler.net | grep -i email
Registrar Abuse Contact Email: [email protected]
Registrant Email: projecteuler.net@...
Admin Email: projecteuler.net@...
Tech Email: projecteuler.net@...
Re:Project Euler has been hacked
by DesmondFlexy on Sunday August 02, 2015 @03:24PM
(#9992026)
Yea, I saw it too.
I would have reported it to someone at project euler but couldn't find any contact information beyond a link to an inactive forum.