So you are saying you use Coinbase and your Coinbase balance went down after you received Bitcoin funds?   And there is a transaction in Coinbase history that shows a BTC withdrawal ("You sent bitcoins to xxxxxxxxxxxxxxxxx") and you did not make that withdrawal request?  And that you have 2FA authentication?

Well, then let's consider what could have happened.

Authy is the 2FA authentication method that Coinbase uses.  Authy requires a mobile app or alternatively the 2FA code for withdrawal is sent as a text message.

So did you receive a text message with a 2FA code from Authy?

Either way, Coinbase can help you figure out exactly when this 2FA code for this transaction was sent (and Authy knows the the IP of the mobile device if the 2FA came from an app), and the IP address that was used when accessing Coinbase.com for that withdrawal transaction .

Have you contacted them?
 - http://support.coinbase.com/customer/portal/emails/new

I'm not able to see the image on postimg.

But if two separate accounts are showing the exact same withdrawal transaction that's something Coinbase needs to know about.

What I'ld like to know is who suffers if Mt. Gox offers Litecoin trading and there is a 51% attack against Litecoin in which those funds were then double spent against Mt Gox.

Mt. Gox was asked this question, but they declined to provide an answer:
 - http://pastebin.com/RVe7LbH9

As a result, it must be presumed that funds are not safe when left with an exchange that trades alt coins and doesn't have a policy or other protections regarding a 51% attack:

Your Bitcoins Are Not Safe At Alt-coin Exchanges
 - http://www.bitcoinmoney.com/post/53207712103

Doh!


Will the existing paste's be restored / made available again?

A race attack (on 0/unconfirmed) uses deception where the Bitcoin node used by the recipient sees one transaction but the miners see a different transaction -- with both transactions spending the same coin.

So if your node were to see one transaction (at 0/unconfirmed) and then eventually a block came in with a different transaction then your node will behave as if the original transaction never occurred.

So there's no alert and no other way to learn that a double spend occurred.

If the race attack failed (i.e., the mining nodes received the same transaction as the recipient's node knew of) then there would be no way for a the recipient's node to know that an attack had been attempted.

Now if there is a block re-org in which a transaction had a confirmation and then a subsequent block arrived causing a transaction to revert to 0/unconfirmed, then that might be visible to someone watching a transaction but the client itself does not alert on such an event.

Some services that have multiple listeners (using a customized client that does not reject invalid double-sped transactions) can recognize double spends, but this detection and alerting is not something the stock bitcoin.org client offers.

Blockchain.info does report double spend conflicts for an address in their web interface.

Blockchain.info
Under the Receive Money tab, select pull-down for actions on any address.  Then click Sign Message.

Doh, sorry!  Fixed.   The link is:
 - http://www.bitcoinmoney.com/post/52305091840

It gets to be diminishing returns.

Like when Dwolla enacted the 30-day probation before transfers could be made to Mt. Gox and other Bitcoin exchanges the result was the "Dwolla <--> Mt. Gox" thread in which person-to-person trading between forum users absorbed much of that demand from those with less than the thirty days.   Then Dwolla proceeded to try to figure out which of their customers were performing these person-to-person trades  and extend the "high risk merchant" status to those accounts.  It is kind of like whack-a-mole.

So banks close the accounts for Bitfloor, Bitcoin-To-Cash, Bitspend, etc.  but at the same time they operate account-to-account (A2A) transfer methods which facilitates person-to-person trading of Bitcoins via the banking system:
 - http://en.bitcoin.it/wiki/A2A_Transfer_Methods

In the U.S., FinCEN's guidance describes trading bitcoins or cash as being a money transmitter.  Money transmitters are required to register with FInCEN as a Money Service Business (MSB).    There is an exception however.  There is a limitation in the regulations for infrequent trading (i.e., five times or less per year, and not done for profit):

Limitation On MSB Regulations For Infrequent Trading
 - http://www.bitcoinmoney.com/post/52305091840

Thus there is then valid reason for (most of) these thousands of traders to be active without regard to FinCEN's guidance.  

In-Person Bitcoin Exchanges Are Thriving
by Jon Matonis



 - http://www.americanbanker.com/bankthink/in-person-bitcoin-exchanges-are-thriving-1060061-1.html?zkPrintable=1&nopagination=1

A 256 bit number stored as a floating point and truncated:
- http://en.bitcoin.it/wiki/Target

Also more info here:

What is “difficulty” and how it relates to “target”?
 - http://bitcoin.stackexchange.com/q/8806/153

Paywall.  Anyone care to provide some excerpts?

Just to clarify, what I'm asserting is that if my e-mail account is compromised an attacker can reset my password and withdraw my funds.

Steps:

From a browser instance after clearing cache, cookies, etc:

Step 1: Confirm 2FA is active (Attempt to login to account in which 2FA is activated, using just username and password).  Response: "Your code isn't valid."
Step 2: Click "Request new password" button.
Step 3: Login using single use login sent via e-mail
Step 4: Once authenticated, click GA_Login tab [Edit: and click "Create code" button.]
"Google Authenticator is enabled for your account. If you want to create a new key - please click on the button below. The old key will be dropped."
Step 5: Add TOTP secret to Google Authenticator, mark "I have successfully scanned the current code" checkbox, and click "Code scanned" button.
Step 6: Withdraw funds using new TOTP secret from Google Authenticator

I see that BitPay is no longer using that BTC/USD market:
 - http://blog.bitpay.com/2013/06/important-update-on-bitpay-exchange.html
 - https://bitpay.com/bitcoin-exchange-rates

Which side doesn't have Internet ... the sender or the recipient (or both)?

From another thread:

If you did that then at this very moment you would be accepting bitcoins at $112 but you might then be trading them at another exchange at $107.  Because of the temporary USD withdrawal halt at Mt. Gox, the price on their market has diverged from others/

When Mt. Gox "was" the market, there was essentially one source for determining price.  Now it might need to be derived with an algorithm, like how BitPay does it:
 - https://bitpay.com/bitcoin-exchange-rates

Is that going to be the Bitcoin equivalent to the "boating accident" that befalls so many precious metals investors?
 - http://www.zerohedge.com/news/how-hide-your-gold-bloomberg-primer#comment-1756269

Posting today an article from June 3rd?    I don't think this board is lacking in articles lately, ... this one wouldn't have been missed.

Please consider packaging it for BlackBerry10 too.

Bitcoin doesn't have to be useful in every situation for it to grow.  If bitcoin were used just for online gambling, or just for remittance payments, or certain other specific uses, that would be enough.  But since Bitcoin can serve all these plus more expect it to permeate other areas as well.    But if your Nascar fan never knows of nor cares about Bitcoin a few years from now, that's not failure.

As far as credit cards giving protection, that's correct and something not available currently (without using escrow).  

But you as a consumer are paying for that.  The difference is that when a merchant includes the cost of the payment card fee into the price, every customer pays the higher price regardless of payment method used.  So currently, credit card customers are being subsidized by customers paying cash.    But certain types of business that are considered high risk already pay a higher rate, and they will be among the first to have an incentive to accept bitcoin and pass along the savings to the customer.

High Risk Merchant Accounts
 - http://bitcointalk.org/index.php?topic=73694.0

So when you pay for an airline ticket with credit card the fare is several percent higher than it should be.  So if your ticket is $400 with credit card or the equivalent of $388 with Bitcoin, and it is a non-refundable ticket anyway, what payment method are you going to choose?

So then those that still choose to pay with credit card do so because they plan to use the customer protection -- thus the cost of fraud on a per-dollar basis rises and the merchant fees have to rise.   It's a self-reinforcing trend.   A larger share of the remaining credit card transactions will be fraudulent, allowing the cash/bitcoin discount to become larger, which pushes more of the non-fraudulent activity over to the cash/bitcoin method.

Additionally, at the restaurant that has "Cash only", I don't get the option to say that I prefer credit card.  If that's the only payment method they accept then that's how I pay.   So when Nascar Bob wants tickets to a sold-out race and the seller only accepts Bitcoin payment, Bob will follow whatever instructions he needs to do to get his tickets.   Today, those instructions could be as simple as: "go to Seven Eleven, pay the cashier exactly NNN.NN dollars for a Moneygram bill payment transaction".  Boom.  Done.  Bob just made a purchase using Bitcoin and still doesn't have to know a thing about Bitcoin.