Conficker Worm Targets Microsoft Windows Systems

Last Revised
Alert Code

Systems Affected

  • Microsoft Windows


US-CERT is aware of public reports indicating a widespread infection of the Conficker/Downadup worm, which can infect a Microsoft Windows system from a thumb drive, a network share, or directly across a corporate network, if the network servers are not patched with the MS08-067 patch from Microsoft.

Researchers have discovered a new variant of the Conficker Worm on April 9, 2009.  This variant updates earlier infections via its peer to peer (P2P) network as well as resuming scan-and-infect activity against unpatched systems. Public reporting indicates that this variant attempts to download additional malicious code onto victim systems, possibly including copies of the Waledac Trojan, a spam-oriented malicious application which has previously propagated only via bogus email messages containing malicious links.

Home users can apply a simple test for the presence of a Conficker/Downadup infection on their home computers.  The presence of a Conficker/Downadup infection may be detected if a user is unable to surf to their security solution website or if they are unable to connect to the websites, by downloading detection/removal tools available free from those sites:

If a user is unable to reach any of these websites, it may indicate a Conficker/Downadup infection.  The most recent variant of Conficker/Downadup interferes with queries for these sites, preventing a user from visiting them.  If a Conficker/Downadup infection is suspected, the system or computer should be removed from the network or unplugged from the Internet - in the case for home users.


A remote, unauthenticated attacker could execute arbitrary code on a vulnerable system.


Instructions, support and more information on how to manually remove a Conficker/Downadup infection from a system have been published by major security vendors.  Please see below for a few of those sites. Each of these vendors offers free tools that can verify the presence of a Conficker/Downadup infection and remove the worm:



Microsoft PC Safety hotline at 1-866-PCSAFETY, for assistance.

US-CERT encourages users to take the following preventative measures to help prevent a Conficker/Downadup infection:

  • Ensure all systems have the MS08-067 patch.
  • Disable AutoRun functionality. See US-CERT Technical Cyber Security Alert TA09-020A.
  • Maintain up-to-date antivirus software.
  • Do not follow unsolicited links and do not open unsolicited email messages.
  • Use caution when visiting untrusted websites.
  • Use caution when downloading and installing applications.
  • Obtain software applications and updates directly from the vendor's website.
  • Refer to the Recognizing and Avoiding Email Scams (pdf) document for more information on avoiding email scams.
  • Refer to the Avoiding Social Engineering and Phishing Attacks document for more information on social engineering attacks.



March 29, 2009: Initial release|March 30, 2009: Updated|March 30, 2009: Updated|April 09, 2009: Updated

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