There is nothing backing it... It is made up.
And yet it is currently exchanging for $31.39, nearly at it's all time high.
And yet there are still people out there who attempt to spread FUD by posting lies. For instance:
quote: Common Misconceptions About Bitcoin – A Guide for Journalists
The Bitcoin price did NOT fall to $0.01 in June 2011.
The backstory behind this myth is an event in June where an administrator account at MtGox, a Bitcoin exchange which had over 80% market share at the time, was hacked, and the attacker managed to manipulate MtGox’s database tables to create a balance of 2 million bitcoins within his account and immediately sold them, consuming all of the buy orders that had been placed on the site in the months before going from $17.50 all the way down to $0.01. However, what sank to $0.01 was not the actual Bitcoin price, but rather a MtGox representation of the price. A price is, by definition, a value in exchange for which something is being bought and sold at a given time. In this case, however, MtGox later rolled back all of the trades that had happened during the event, so no lasting purchase or sale was actually made at anything less than $10. MtGox’s price charts show no transactions happening on the day. Aside from the attacker, no human being was, at any point, willing to sell bitcoins at anything close to $0.01 – the orders that were processed were all made weeks and months before the event, and at exchanges other than MtGox, the price generally remained at a healthy $13-$18. And, most importantly of all, the 2 million BTC that were sold were not even real bitcoins – they were simply fraudulent entries in MtGox’s database. Although it is understandable how some can interpret the event as the price dropping to $0.01, pointing to this incident as a sign of Bitcoin’s price instability is highly disingenuous – the root cause was a security mishap at a third party service, not a sudden loss of confidence in the currency. Incidentally, if the MtGox hack does count as the Bitcoin price dropping to $0.01, then another, less known, MtGox glitch deserves to count as the Bitcoin price reaching $1 billion.
Hackers may successfully attack third party sites. And they have done so in the past. The bitcoin protocol, however, is secure, and as I've repeatedly stated, is based on very strong crpytography that would take billions of years to crack with current technology. Not only that, but the crpytography can be upgraded if necessary.
People don't honor bitcoins for real currency if there is a mass run to withdraw funds