[PhantomPhreak]

Bitcoins were sent by the Bitcoin community to an unspendable address (1CounterpartyXXXXXXXXXXXXXXXUWLpVr, which has no knowable private key), and the Counterparty protocol detects this and creates XCP in proportion to the destroyed bitcoins, crediting them to the sending address. (This was only for the month of January... don't send any bitcoins to that address now!)

[officialjunk]

what is the significance of the tail end ...UWLpVr? why not just X's all the way?

[178]

Every Bitcoin address includes a checksum at the end, so while you can make up any address like in this example, the checksum still needs to be correct in order to form a valid address. It's a great feature against typos, btw.