I have just sent bitcoins from one account of mine to another, and after I sent it I checked on blockchain.info to get updated about confirmation. There, I noticed something peculiar, it said that I made two transactions at the same time, when I made only one. The first transaction was to the correct address and the correct amount. But the second transaction was not one that I made. The second thing I noticed is the SUM of both transactions, together they form the exact amount I last received to this account a few days ago. This looks to me like a hack. At this moment these transactions have net yet been confirmed, can I do anything about it? Can a transaction be created fraudulently and accepted by the miners? How can a hack like this be accomplished (if it is a hack).
You are not being hacked. These are not two separate transactions; it is one transaction with two outputs. The second output was automatically created by your wallet client and sends back to a new address which also belongs to you. This is a normal and necessary feature of how Bitcoin works, called "change". See How does change work in a bitcoin transaction?
If this transaction were malicious, it would mean that someone had access to your private key; if so, they would also have stolen your earlier transaction. Moreover, they would have stolen the coins as soon as they obtained the key; they wouldn't have waited for you to make your own transaction.
protected by Community♦ Feb 15 '18 at 19:55
Thank you for your interest in this question.
Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
Would you like to answer one of these unanswered questions instead?