Hi,
Recently using Bitcoin Core I send BTC to two addresses simultaneously. Transactions look something like below after submit. There are two entries, one with Output index: 2 and one with Output index: 0

For both entries the transaction ID is the same. The strange thing is that when I look up information on the transaction on blockchain.info I see that additional BTC are send to a third address. I don't know that address.

The balance of my Bitcoin Core client is also different from what I can see on blockchain.info. The difference is the amount send to the third address. I expect that I will not be able to use my blockchain data anymore because it has my original transaction which is different from the transaction that got added to the public blockchain.

My conclusion now is that the transaction I submitted was changed by someone after I submitted it to the Bitcoin network. This baffles me. Around 20% of the total value of the transaction was skimmed / stolen from me.

How is this possible? How can they change my transaction?

Is it possible to prevent hacks like these? Is the Bitcoin Core client hacked? Is it safe to use?

What about the Output index: 2 and one with Output index: 0 ? Could it be that there was also a Output index: 1? For the third address?



Status: 0/unconfirmed, in memory pool, broadcast through 7 nodes
Date: ****
To: Wallet #1 *****************
Debit: -********* BTC
To: Wallet #2 **************
Debit: -******** BTC
Transaction fee: -0.00002341 BTC
Net amount: -********** BTC
Transaction ID: ***************************
Transaction total size: 468 bytes
Output index: 2

Status: 0/unconfirmed, in memory pool, broadcast through 7 nodes
Date: *************
To: Wallet #1 *********
Debit: -***** BTC
To: Walllet #2 **********
Debit: -************ BTC
Transaction fee: -0.00002341 BTC
Net amount: -****** BTC
Transaction ID: ********************************
Transaction total size: 468 bytes
Output index: 0