Ah, I get it. So, they can spend my coins that where already in the wallet at the time of the backup / or before I changed the password (that part I didn't get straight), but they cannot spend the new coins that arrive there.
Thank you. The old wallet was hacked actually and they took some coins :/ ... but I have a miner still sending coins there (I'm going to change it after a few blocks) and I was afraid they could also get my new stuff.
Thanks again.
If someone has compromised your wallet it means they have control over your private keys of those addresses and thus any BTC in there currently and any BTC that goes there in the future as well. If I were you I'd redirect my miner away to another address asap as all you are doing is giving free BTC away.