Blaster worm attack a bust

Error in worm design, last-minute action by Microsoft cut short attack

A scheduled denial-of-service attack against Microsoft Corp.'s main software update Web site didn't materialize over the weekend, as computers infected with the W32.Blaster worm failed to find their target.

Blaster first appeared Aug. 11 and quickly spread to computers worldwide by exploiting a known security vulnerability in Microsoft's Windows operating system (see story).

By Aug. 15, the worm, which targets a Windows component for handling remote procedure call protocol traffic called the Distributed Component Object Model interface, spread to more than 423,000 systems, according to Oliver Friedrichs, a senior manager at Cupertino, Calif.-based antivirus vendor Symantec Corp.

In addition to infecting vulnerable Windows machines, the Blaster worm was programmed to launch a denial-of-service attack starting Aug. 16 against, an Internet domain owned by Microsoft and used to distribute software updates to Windows customers.

However, an error in Blaster's design, combined with last-minute actions by Microsoft to change the registration of, cut short that attack.

Blaster's author provided the incorrect domain address for windowsupdate. The address specified in the worm's code,, simply forwards users to the actual Windows update site,, according to Mikko Hypponen, head of antivirus research at F-Secure Inc. in Helsinki.

On Aug. 14, Microsoft delisted the domain name, calling it a "nonessential address."

That solution also removed the threat of collateral damage from the attack, because requests for would never leave infected machines, slowing down the Internet, according to Sean Sundwall, a Microsoft spokesman.

On Aug. 16, Microsoft didn't detect any irregular network activity associated with the Blaster worm, Sundwall said.

The Bethesda, Md.-based SANS Institute's Internet Storm Center reported Aug. 16 that the denial-of-service attack anticipated from Blaster had been avoided.

The number of Blaster infections is also down more than 80% since the worm's peak last Monday, indicating that vulnerable computers are being cleaned and patched by their owners, Friedrichs said. Symantec expects that trend to continue, he said.

In time, Blaster will join predecessors such as the Code Red and Nimda worms, inhabiting a small population of infected machines that pose a risk to new, unpatched systems, but not spreading much beyond that, he said.

For Microsoft, the Blaster worm outbreak stoked internal efforts to shore up vulnerable services.

Even though Blaster missed its target, future worms might be smarter, faster and more destructive, Friedrichs said.

Microsoft is using the occasion to take "a number of steps" to protect valuable customer services such as the Web site from attack, Sundwall said. He declined to provide details of what changes the company is making.

Microsoft is also using the Blaster outbreak as an impetus to improve communication with consumers about the need to patch regularly, Sundwall said.

"We learn from every worm out there. What we learned from [Blaster] is that there aren't enough consumers who installed the patch and use [Windows] auto-update," he said.

Microsoft customers should expect a concerted effort by the company to reach out in coming weeks and raise awareness of the need to patch vulnerable systems, he said.

Copyright © 2003 IDG Communications, Inc.

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