[Codestare]

Think of 'owning' a bitcoin as 'having the ability to spend' this bitcoin.

This ability is guarded by a private key. If this private key is stolen, someone else ALSO has the ability to spend this bitcoin.

Then, if this attacker transfers this bitcoin to another of his own private keys (he 'spends' it), in the blockchain there will be a record, yes. But who owns this new private key is unknown.

[huherto]

Thanks that was very clear. Follow up question. Could criminals use bitcoin as a payment method for ransom ?

[sergers]

yes and they do.

all the ransomware in the news in recent year or two accepted bitcoin payment to decrypt your data.