In the past (2011) I had a wallet with address: 182TnmtTAStyMyBgAMBrRKNbtC1JqgC6Hp
I bought 1 BTC and spent it. Nothing strange here.
Then I bought 4 BTC and did nothing with it.
Then after some months (in the beginning of 2013) I saw that the 4 BTC were transferred without my knowledge.
Maybe somebody here can explain this?
Are they stolen somehow or transferred to another address within my wallet?
At that time I had a offline wallet (wallet.dat) on my computer which I still posses on a USB stick.
This is the transaction id: 8c11f74362e52c563089125516fabe82907d8469c49d34edc5f8eaaa88eb445a
It doesn't look like it has been transferred to an adress of your wallet, but rather some kind of mixing service / 3rd party, due to the long chain of transactions that follows. I'd say it is more likely that the funds were stolen.
Did you create the wallet.dat yourself or did you use a thirdparty to create the privkeys for them? That could be the reason, other then that, i couldn't imagine how your BTC got lost.