Mt. Gox, the world's largest Bitcoin exchange, is delaying plans to support a new form of virtual currency known as Litecoin following a series of debilitating Internet attacks that are growing increasingly powerful.

The most recent distributed denial-of-service (DDoS) attack to hit Mt. Gox came on Sunday, and it knocked the Tokyo-based exchange offline for four hours, officials said in a statement issued Wednesday. Unlike more traditional DDoS attacks, which flood websites' routers and servers with more junk data than they can handle, the latest assault targeted Web applications the Mt. Gox site uses to process and secure customer transactions. That's known as Layer 7, or the application layer, of the networking stack.

"What we are experiencing lately are 'Layer 7' DDoS attacks," the statement read. "Unlike your average DDoS (which overloads the servers with traffic to the sites as a whole) these are much more creative and harder to detect in that they target specific elements of the site and make it difficult to distinguish malicious traffic from normal traffic. The attackers' goal is to shut down the exchange, either thorough the DDoS itself, or by forcing Mt. Gox to take measures that have the same effect."

Mt. Gox officials didn't elaborate on the details, but the attacks are consistent with techniques that have emerged over the past 12 to 18 months. DDoS campaigns hitting more than a half-dozen of the world's largest banks over the past six months have used a relatively new tool known as "itsoknoproblembro." Attackers install it on powerful Web servers that they've commandeered and then use it to direct a rapidly changing array of methods that target multiple parts of a target's infrastructure.

The Layer 7 attacks frequently target sites' HTTP, and HTTPS protocols, which overwhelm the applications used to deliver webpages and cryptographically secure transactions. These "logic" applications are often prone to bottlenecks that are vulnerable to large and sudden torrents of data, especially when that data has been manipulated or corrupted. As Ars recently reported, one particularly potent attack targeted an unidentified site's login page by unleashing a script that entered a legitimate user name along with passwords that were known to be invalid. When repeated millions of times, the technique can overwhelm targeted systems as servers perform database lookups, report the authentication failure, and then record it in internal logs.

In light of the repeated attacks, Mt. Gox officials have decided to delay adding Litecoin, the digital currency competing with Bitcoin. Litecoin is based on the same peer-to-peer protocol as Bitcoin, but it targets a faster block rate, allowing it to be mined by people with consumer-grade equipment. Among other things, it uses scrypt as the primary hashing algorithm, making "proof-of-work" tasks easier to carry out on less-sophisticated computers than Bitcoin requires.

"We were planning on doing so two weeks ago, but events derailed that plan," the officials said in the statement. "Right now we are focused on overall stability of the exchange and will launch LTC when we are ready. Otherwise we could be further complicating things."

Company engineers are building an IT infrastructure and a new trading engine, which are slated to be completed by May and June respectively. The exchange has also contracted with Prolexic, a Florida-based provider of DDoS mitigation services. Mt Gox keeps at least 90 percent of its Bitcoin holdings in "cold storage," meaning they aren't available on the Internet. That means that even if hackers find a way to penetrate Mt. Gox servers, they will at most be able to steal only a fraction of the reserves. (DDoS attacks, while disruptive, don't give attackers the ability to breach a target's defenses or steal its assets.)

"Bitcoin and other cryptocurrencies are just now entering the consciousness of people around the world, and still have a long way to go towards greater acceptance," the statement said. "While these attacks are a nuisance and a disservice to all Bitcoin holders and enthusiasts, they are also part of the growing pains of this incredible new technology."