UltraDNS, a managed domain name service (DNS) service owned by NeuStar, went offline on Tuesday because of a distributed denial of service attack, reports NetworkWorld magazine.

Early this morning, our monitoring systems detected a significant denial of service attack, which affected a small subset of our customers, in some cases for as long as a few hours.

According to UltraDNS competitor Dynamic Network Services, which first reported the outage, the downtime impacted big UltraDNS customers such as Amazon.com (s amzn), Salesforce.com (s crm), Advertising.com and Petco.com. It came on the heels of a DDOS-induced outage at GoGrid that was launched Monday afternoon.