Hello, I hope someone can help. I recently opened a new account an an trading website: Poloniex.com. Before this, I only made an account for Bitcoins using a immediate card purchase and kept it all on a online wallet. Yesterday, I made a withdrawal from the wallet into my Poloniex account and paid all the fees etc. And today I checked, the wallet is empty. And I checked my Poloniex and the amount it there. BUT this is the problem:
When I checked the address I sent to, the blockchain shows that all the money I sent there is GONE, sent to someone else. I have sent a support to stop it before confirmation but does anyone know what I can do?
As long as your balance in the exchange is still the same then you are safe.
Elaborating on what buwaytress said, your address is specific to you, however, this is an online address and if an exchange as large as poloniex left all coins on nodes with internet access then they would be a lot easier to hack than offline addresses. Therefore, automatic scripts run on their nodes to ensure your deposit is first counted and then the coins from that address are stored offline (usually in a printed paper wallet once an address has got enough coins in it - depending on what the threshold is).