What happens to the original bitcoin after a wallet restore? I'm thinking of buying some bitcoins. Before I do I want to be sure that I can backup and restore my wallet - Bitcoin Core. This seemed to go ok, the bitcoin loaded into the new wallet which was on a different computer from the original.
The original bitcoin wallet still shows the old balance.

I'm sure it's unlikely, but what if someone stole my computer and I then restored my bitcoin to a new wallet - would the thief be able to spend from the original wallet after I'd done the restore?
I'm sure it's unlikely, but what if someone stole my computer and I then restored my bitcoin to a new wallet - would the thief be able to spend from the original wallet after I'd done the restore?


Yes. The two wallets 'hold' the same Bitcoin. If the thief steals your original wallet, it becomes a race to see who can spend the Bitcoin first. You have the advantage that only you know your password. (You did set a password, right? :) The thief has the advantage of surprise.

Additionally, if you generate a new address on the backup of the stolen wallet, the thief will have access to that too. This is due to the 'keypool' feature of Bitcoin. To avoid this, after your wallet is stolen, make an entirely new wallet, and transfer your Bitcoins to that. That will be safe, assuming you win the race.