Internet advertising company DoubleClick was shut down by a denial of service (DoS) attack launched from computers on the Internet, a company spokeswoman said.
The attack crippled the company's website and its advertising servers, which distribute web advertisements to other sites on the internet. Ripple effects from the attacks were felt across the internet, as web pages that display DoubleClick ads struggled to retrieve them from the company's servers, causing "severe disruption" for its customers, according to a company statement.
Leading websites all experienced significant slowdowns during the period covered by the attack, including web pages for the Washington Post, New York Times, Cnet Networks, Nortel Networks, and Infoworld Magazine, according to web performance measurement company Keynote Systems.
Keynote measurements for the period of the attacks showed the "base page" - or basic HTML documents - served by those websites loaded quickly, but the "full page", which includes any content the web page points to, suddenly began to load very slowly, said Lloyd Taylor, vice-president of operations at Keynote.
DoubleClick's DNS servers were targeted in the attack, which came from "outside sources" that the company has yet to identify, and lasted for about four hours, said Jennifer Blum, vice-president of corporate communications at DoubleClick.
DNS is the system of servers that matches reader-friendly names such as DoubleClick.net with the numeric IP addresses used by machines on the internet to route traffic.
Keynote recorded a threefold slowdown in response time for web pages lasting four hours. The company does not know what the source of the slowdowns was, but the behaviour of the pages was consistent with a DoS attack on DoubleClick, Taylor said.
Paul Roberts writes for IDG News Service