What — a — day.

It all started this morning when, from Twitter Status, this nugget of good news arrived, explaining the odd, intermittent service:

We are defending against a denial-of-service attack, and will update status again shortly.

For those of you (like me) who didn’t know what a Denial-of-Service or DoS Attack was at the beginning of the day, you probably know what it is now. The U.S. Computer Emergency Readiness Team (CERT) defines a DoS Attack as the following:

In a denial-of-service (DoS) attack, an attacker attempts to prevent legitimate users from accessing information or services. By targeting your computer and its network connection, or the computers and network of the sites you are trying to use, an attacker may be able to prevent you from accessing email, web sites, online accounts (banking, etc.), or other services that rely on the affected computer.

The most common and obvious type of DoS attack occurs when an attacker “floods” a network with information. When you type a URL for a particular web site into your browser, you are sending a request to that site’s computer server to view the page. The server can only process a certain number of requests at once, so if an attacker overloads the server with requests, it can’t process your request. This is a “denial of service” because you can’t access that site.