I was using Bitcoin Core(non password protected) and MyCrypto was password protected.
Then all they required was a copy of your wallet.dat file to get access to your Bitcoins... Without a password on it, anyone with a copy of your wallet.dat would be able to access the private keys and create transactions sending the bitcoins wherever they wanted.Do you store a backup of your wallet.dat on a cloud-based backup server like OneDrive, Google Drive, DropBox etc?
Or perhaps you sent yourself a copy of your wallet.dat to your email as a backup? Interestingly... the BTC address (12P5MtCHoyTJdJitAWSDkeb5fYHSQj7X3X) that the bulk of your coins got sent to, is tweeted by a "Bens Bitcoin Consulting LLC"... seems they also had funds stolen from them that went to the same address (but from Exodus wallet):
https://twitter.com/ben92994350/status/1288107762048577538
I already changed, my passwords and created new wallet.
And transferred cents that was left there in my wallet to new wallets.
If you never stored your wallet.dat backup online, then my guess would be malware of some description that has leaked your wallet.dat and/or your MyCrypto login credentials. I would consider the entire machine compromised... I would not be surprised if the thieves already have the details for your new wallets.And transferred cents that was left there in my wallet to new wallets.
I would recommend that you format the PC and reinstall the OS.
If you stored your wallet.dat on a cloud server of some sort, then it's likely that your account on the cloud server was compromised. You'll need to change ALL your passwords.