Distributed denial of service (DDoS) attacks are an unfortunate fact of life on the web. These attacks can be hard to stop once they occur, but did you know many dedicated server hosts provide protection against them?
This service usually takes the form of a firewall or dedicated proxy, and can be costly. Popular websites are prime targets, however, and if your site generates enough income to justify the expense, DDoS protection is well worth the money.
Some attacks are so advanced they can bypass preventive methods. These are less common and are generally used on mega-sites like Twitter, though. If anything, be sure your host provides good customer service. A responsive support team is often the best method for fighting a DDoS attack.