My LTC coins are stolen, my wallet was password protected my PC is also passworded!

Hello, I am extremely nervous because my 150.4 LTC have been transferred to an address that I do not know.
PC and Wallet are provided with a password.
At 2:44:10 pm on 2:10:10 pm a transfer was arranged to the address:
Lfdi63MVmnemTxPPdQj7wdCRYSDx9U9FHC
I can not select transaction, the field is greyed out.
The last use on the PC with the Wallet version 8.7.5.
On 11.12.17 I have activated my system, running virus protection and Windows updates … Since then I have updated my Wallet Core to version 5.7.1.
I do not understand the process and not the possibility of theft?
My address is:
LbgTQjXre58mB2Bth76c9EyiaizxH6Hukz
the Balance is 0 LTC
My last name is deposited under name. I last received 30 LTC on 24.4.2015 at 12:07
BG Thomas

Hello, of course I can guarantee that I generated the first Litecoins myself. The purchase of other LTC I can also prove I still have the bank statements. All LTC inputs I can prove conclusively. To the transmission of the data, I would like to contact you directly. Can you help me?

Is it possible to decrypt an encrypted wallet. dat (password depth: 12 characters)? Or about importing it into a new Wallet. dat? I’m trying to understand the theft.

Yes, there are programs that can do that.

also

Yes, its pretty easy to restore an wallet.dat on another PC.

Sorry for your coins, I think somebody got control of your wallet.dat or hacked your pc real good. or BOTH.

No, my PC was not hacked.
Thanks for the message. That means, only a stolen wallet. dat has put me in this unpleasant situation everything else is to be ruled out?
I was able to transfer my Litecoins up to the platform https://bittrex.com/, to the address: Track LPiSTbThjYY39gvcYB4DsNZXevSd84aEpQm. Do I have other options or do you have any tips?

To me it looks like it was.

somebody got access of your wallet and figured out your password… how this was done, I can just think of many posible ways but you will never know 100%.

I dont think you have too many options, did you download some program or tool, and when you try to run it, nothing happend? (usually this is how you get hacked)

No, my system was only set up for the Litecoin Wallet software, with current updates and anti-virus software. That’s all they did with it. For security reasons.