Akamai, Limelight, Level 3 and a number of companies help Web sites fight against DDoS attacks and unexpected traffic. But their services are prohibitely expensive, starting at $15,000 a month.

CloudFlare, a San Francisco start-up, offers a similar service on the cheap. It distributes a site's traffic across its many data centers and can quickly recognize and filter out a DDoS attack before it hits a company's network.

It offers basic services for free and charges more for premium services like additional security or site management.

Most customers pay $20 a month, though its largest enterprise customers pay as much as $2,000 a month.