It looks like, using just the 17nu address here:
Only 2 transactions occurred. This transaction:
Resulted in the UTXO for 1 BTC to 17nu.
That UTXO was then used in this one:
But it was combined with other transaction unrelated to the wallet. I'd say your wallet was compromised. Your transactions got bundled in with other UTXO's elsewhere not related to your wallet.
The address it was sent to:
had a flurry of activity on 5/6/14 within a 2 hour time period. In some cases with massive bundling of UTXO's. 34 inputs, 56 inputs. The transactions moving BTC from that wallet out left it with a zero balance.
Almost all of this funnels into address 17gH1u6VJwhVD9cWR59jfeinLMzag2GZ43:
Which processed 17,990 transactions between March 2014 thru October 2014. The entire wallet was left empty with 120,347 BTC passing through it.
Either this address is used to launder BTC or simple as a convergence point for distribution. Either way this address is tied to a number of google search results in people getting hacked. Eg: https://bitcointalk.org/index.php?topic=754624.0;all
Final answer. You were hacked in some way.
Note: I added all the text in here to show how i traced his BTC from his address to an address known for hacking. This was to demonstrate how i came to the conclusion it was a hack and not an anomaly, software error, bug or something other.