The attack caused problems for more than two hours--from 5:30 a.m. to 7:45 a.m. PDT. Many of the world's most popular sites suffered from widespread outages, according to Keynote Systems, which compiles statistics related to Web surfing. On a typical day, the top 40 sites measured by Keynote rarely dip below 99 percent availability. On Tuesday, however, Keynote saw availability drop to 81 percent.
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A denial-of-service attack rattles a key Internet service at Akamai and knocks Yahoo, Google and others offline temporarily.
The attack caused problems for Web surfers for about two hours. It's taking a lot longer for the affected companies and Internet monitoring firms to get to the root of the problem.
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An Akamai spokesman said it noticed an attack against four unnamed "customers" that rendered their sites inaccessible. Akamai said the strike against those customers in turn caused a failure of its own domain name server (DNS) system, which translates word-based URLs into numeric Web addresses to link surfers to company sites.
"We do know that attack was against four sites that happened to be Akamai customers," company spokesman Jeff Young said. "But I don't know if the intent was to go after Akamai or go after Web properties that happened to be customers of ours."
Tuesday's outage comes nearly a month after, causing some slowdowns.
Other parties may not agree with that assessment. Keynote earlier Tuesday reported the Akamai DNS system outage and speculated that Cambridge, Mass.-based Akamai was the target of a denial-of-service attack, which then caused the Yahoo, Google, Microsoft and Apple sites to fail.
Dug Song, security architect for network security company Arbor Networks, said the outage appeared to be an Akamai problem. During the outage, Song noticed that sites such as Google were still functional, but someone typing www.google.com couldn't get to that site, because the address would not translate into its numeric Internet Protocol code.
"It was definitely some sort of Akamai issue," Song said in an interview. "Their name service for all these major sites stopped working. You couldn't reach these sites, even though the sites were up. You just couldn't get to them because the name resolution wasn't working."
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In a recent incident, the Netsky virus used such a technique to and other file-sharing networks, disrupting service at some. Earlier in the year, the main Web site of thewas crippled after attacks from computers infected by the MyDoom virus.
On Tuesday, David Krane, a spokesman for Google, confirmed that the search site was "affected for a short period of time earlier today" and that all systems have been restored. Krane said Google was not the target of a denial-of-service attack.
Microsoft also confirmed that its sites were affected but added that it was "deferring to Akamai for additional information on the reported outage."
With the sites back up, it appears that the DNS issue has been resolved. But Yahoo's, launched Tuesday, continues to have problems.
Since early Tuesday morning, users have been reporting glitches with Yahoo Mail such as site inaccessibility, slow page loads and inoperable buttons on the site. A Yahoo spokeswoman said the company is "investigating the potential impact of a widespread DNS issue on our services." But launch-related bugs are also a possibility.
"As we upgrade tens of millions of Yahoo Mail accounts for consumers worldwide, some users may experience temporary fluctuations in the service, as we update our systems," Yahoo spokeswoman Mary Osako said. "We expect Yahoo Mail accounts to resume to normal after the upgrades are completed."
Representatives of Apple were not immediately available for comment.