My backup was stolen

[BIGMERVE]

I keep my backup wallet on a thumb drive. Like an idiot I took that flash drive to school and left it in the computer lab. What can I do to make sure the backup isn't used if someone who knows about bitcoin finds it?

Update: I used piper67's advice and was able to fix everything. Thanks for all the suggestions.

[vampire]

I keep my backup wallet on a thumb drive. Like an idiot I took that flash drive to school and left it in the computer lab. What can I do to make sure the backup isn't used if someone who knows about bitcoin finds it?

Create a new wallet, send all the money from the old to the new one.

[unclescrooge]

Create a new wallet, send all the funds of your lost backup on this new wallets.

Quick

Edit: You got me Vampire

[Piper67]

Create a new wallet, send all the funds of your lost backup on this new wallets.

Quick

Yup, yesterday!

[CIYAM]

In short as others have stated move the BTC into a new wallet.

In detail first make sure you have another backup of your wallet then:

1) Remove wallet.dat and start the client (to create a brand new wallet).

2) Create an address to receive coins with and copy it somewhere.

3) Shut down bitcoin-qt and create a backup of the new wallet (be sure not to confuse wallet this with your original one).

4) Restore your original wallet then restart bitcoin-qt and send a small amount of coin to the new wallet address (to test you're doing it right).

5) Shut down bitcoin-qt and create another backup of your now modified original wallet (although this backup is not really necessary).

6) Restore the new wallet, restart bitcoin-qt and check to see that the sent coins appear in it after the blockchain has been caught up.

7) Shut down bitcoin-qt and take another backup of your new wallet (also not really necessary but might save a little scanning time).

Restore backup your modified original wallet, restart bitcoin-qt and now send the rest of the coins to the address from the new wallet.

9) Shut down bitcoin-qt, restore your new wallet backup and after restarting all your coins should appear after the blockchain has been caught up.

If the new wallet does not seem to see coins sent to it (in steps 4 or you may need to perform a "rescan". Also use blockchain.info to verify the new wallet address balance.

Hope this is of some help (and just in case I've got something wrong with the above please wait for a couple of replies for corrections).

[Piper67]

In short as others have stated move the BTC into a new wallet.

In detail first make sure you have another backup of your wallet then:

1) Remove wallet.dat and start the client (to create a brand new wallet).

2) Create an address to receive coins with and copy it somewhere.

3) Shut down bitcoin-qt and create a backup of the new wallet (be sure not to confuse wallet this with your original one).

4) Restore your original wallet then restart bitcoin-qt and send a small amount of coin to the new wallet address (to test you're doing it right).

5) Shut down bitcoin-qt and create another backup of your now modified original wallet (although this backup is not really necessary).

6) Restore the new wallet, restart bitcoin-qt and check to see that the sent coins appear in it after the blockchain has been caught up.

7) Shut down bitcoin-qt and take another backup of your new wallet (also not really necessary but might save a little scanning time).

Restore backup your modified original wallet, restart bitcoin-qt and now send the rest of the coins to the address from the new wallet.

9) Shut down bitcoin-qt, restore your new wallet backup and after restarting all your coins should appear after the blockchain has been caught up.

If the new wallet does not seem to see coins sent to it (in steps 4 or you may need to perform a "rescan".

Hope this is of some help (and just in case I've got something wrong with the above please wait for a couple of replies for corrections).

Or open an account with blockchain.info, create a wallet there, transfer all your BTC to it, wait for the confirmations, delete your wallet.dat, start Bitcoin qt again and transfer the coins back 

[CIYAM]

Or open an account with blockchain.info, create a wallet there, transfer all your BTC to it, wait for the confirmations, delete your wallet.dat, start Bitcoin qt again and transfer the coins back 

Hmm... this does seem a little easier actually. 

[CIYAM]

Also perhaps more importantly (to prevent this from occurring again in the future) *encrypt* your backup wallets!

[BIGMERVE]

Thanks for all the help everyone. I'll make sure I take security even more seriously from now on. Looks like nothing was stolen, which is amazing since I had actually written BTC on the back of the flash drive.

[greyhawk]

since I had actually written BTC on the back of the flash drive.

Yeah, don't do that.

Use something like "wedding anniversary photos" or whatever noone would like to look at.

[Raoul Duke]

Import all private keys to MtGox. They'll make sure to sweep all funds that may arrive to any of those addresses at a later date to one of theirs and credit your account.

[DannyHamilton]

DELETED - I deleted this post to avoid spreading around my stupidity.  Not sure why I misunderstood how this works.

[rate5]

Import all private keys to MtGox. They'll make sure to sweep all funds that may arrive to any fo those addresses at a later date to one of theirs and credit your account.

+1 this is a awesome feature at MtGox

[Kupsi]

Perhaps in a future release of the bitcoin client it might be a good idea to maintain an extra 100 or so pre-generated addresses in the wallet and just have the wallet grab one of these addresses (and generate a replacement) for change?

It does that.

[Raoul Duke]

Import all private keys to MtGox. They'll make sure to sweep all funds that may arrive to any fo those addresses at a later date to one of theirs and credit your account.

+1 this is a awesome feature at MtGox

I wish Armory did that

[DannyHamilton]

DELETED - I deleted this post to avoid spreading around my stupidity.  Not sure why I misunderstood how this works.

[Kupsi]

Perhaps in a future release of the bitcoin client it might be a good idea to maintain an extra 100 or so pre-generated addresses in the wallet and just have the wallet grab one of these addresses (and generate a replacement) for change?

It does that.

I have an encrypted wallet.dat backup from half a year ago, and want to recover its content.

If you used more than 100 keys since the backup was made then any tx past the first 100 are irrevocably lost.

You can't both be right.  Which one of you is wrong?

We are both right.

Edit: What DeathAndTexas meant was: If you used more than 100 keys since the backup was made then any tx past the first 100 after the backup are irrevocably lost.

[DannyHamilton]

You can't both be right.  Which one of you is wrong?

We are both right.

I clearly misread that post.  Sorry about that.

For some reason I was sure I had seen a post indicating that if you've used up the 100 pre-generated addresses, created a backup, attempted a new transaction that had change, and then restored your backup, you would lose that change.  I thought it was the one I posted, but obviously not.  Now I can't find the post. Perhaps I just misunderstood what I had read, wherever it was.

[Kupsi]

No problem