What happened to my coins, hacked? I'm new to bitcoin, downloaded the bitcoin.org client, encrypted my wallet, and purchase a few bitcoins (5.25), for learning purposes.  But now my coins seem to have disappeared to an unknown address.

You can follow the chain here:
http://blockchain.info/address/14Z4C6Bu2DXHcaRkoqKDhY72BE74PRA8Vt

Here's what I did:


Purchased 5.25 BTC from online exchange
Sent .01 BTC to my Armory address for a test
Sent .095 BTC back
Sent .01 BTC back to my Armory address again
Sent .095 BTC back again


And in my bitcoin client it showed all these transaction correctly (screenshot below).  Today I ran it and it seems my blockchain files are corrupted so I start downloading the blockchain again. Meanwhile I check blockchain.info on my address and find that actually when I did my first transaction, (.01BTC) at the same time the entire balance of my wallet was sent to some mystery address (16oc97Z4RRRanyt8bB3RT84XSemZL7KXkg and coins have since been transferred again to another account which would appear to rule out the idea of me randomly sending them to the wrong address).

I swear I checked the blockchain details religiously for the week after my initial transaction and this transaction was never there!

Where did this transaction come from?  It never showed up in my bitcoin client, even though I kept it synced for weeks after my initial transaction.  Were these coins somehow hacked?

I was using my own private computer at all times (and never any online wallets etc...)  I have various antivirus/firewalls installed.
Don't worry, you've not been hacked. This is just one of your wallet's change addresses:

https://en.bitcoin.it/wiki/Change
How does change work in a bitcoin transaction?
Why does Bitcoin send the &quot;change&quot; to a different address?