A few minutes ago I received 0.00000001 BTC. I don't know who sent them or why.

But what makes it crazy is, this sum was sent to an address I do not own and which the client I'm running (the standard Bitcoin-QT, versione 0.8.5) had never heard of before. I know this for sure because I only created 2 (two) addresses using this client, and the receiving address of this transaction is not one of them.

How is this possible at all?  

Is it a hash collision, or what else?

The address is `1Cz2AmLe8U52KR549d13JQkqsqkV64RchB` and the transaction ID is `b9591410ff030e40deb3eda9d2fe30a29642ede443f354bb5f4ed5bb55f0d36d`.

According to [this page](http://blockexplorer.com/address/1Cz2AmLe8U52KR549d13JQkqsqkV64RchB), the address seems to have received money a little time before from `1HTawQNCS4axPXft6L6fkzrv5ya7TguqwD`, which actually *is* one of my addresses; the last two transactions are me sending all my BTCs to a new address, just to be sure. This worked, so it looks like I'm actually the owner of that address, even if my client doesn't list it as one of mine.

What's *exactly* going on here?