^{I've split this into a separate topic from here: https://bt.irlbtc.com/view/254489.0}

Event:

I recently received 0.001 BTC to an address, which I didn't even know I had - after some digging, I realized it was a "change" address, which was technically "public" on the blockchain since 2013 May, but which I never ever purposefully gave to anyone.

The only possibility, how someone could have known this address, is to "find" it on the blockchain.

The transaction, in which I was sent 0.001 BTC https://blockchain.info/tx/f6f2e613f6653a3b47f92fd70ff4d1ccc847811294f734a5e9f310c5b9eb063a , also included hundreds of 0.001 BTC sent to other addresses (and a few larger sums too).

I have several hypothesis on why this was done:

1.
Someone is trying to create confusion and scare people, by trying to make them to believe, that an address collision has happened. This hypothesis is reinforced by the facts that:
a) the first 3 answers were "maybe it's a bug", "maybe it's an address collision", "it's definitely an address collision - this has happened before";
b) when I even suggested the idea that this could have been done on purpose, I was immediately called "naive" and "paranoid" and that I "probably won it on satoshidice and forgot about it".

2.
Someone is trying to "launder" his/her bitcoins, and even goes to the extreme of sending some BTC to random people, to better hide the money trail.

3.
Some sort of denial-of-service-attack/network-spamming?
a) I don't think so, because to spam the network you could send BTC back and forth between the addresses that you own, there is no need to send BTC to other people.

To make some things absolutely clear:
1. Address collision did NOT happen.
2. I did NOT use this address anywhere - the ONLY way it could have been found, is on the blockchain.