Microsoft's latest round of patches released on Tuesday includes an optional update that will shut off the "autorun" capability for users of older Windows operating systems, a move the company has made to reflect the resurgence of worms carried on removable media.
Autorun is a feature that will automatically launch programs that are contained on removable media such as CDs, DVDs or USB sticks. It was designed for the convenience of users, but it also has been used by malware writers to force their malicious code onto victim's computers, with notable examples being the Stuxnet and Conficker worms.
With the launch of Windows 7, Microsoft made a change in how autorun and a related feature, called autoplay, behaved compared to previous versions of Windows. To reduce the risk from worms, autoplay in Windows 7 didn't present an option to autorun programs contained on non-optical media.
With the launch of Windows 7, Microsoft made a change in how autorun and a related feature, called autoplay, behaved compared to previous versions of Windows. If a USB stick is inserted into a Windows 7 computer, the OS won't give an option to autorun its content.
Later in 2009, Microsoft made an update available that would make the same changes to autoplay for Windows XP, Windows Server 2003, Windows Vista and Windows Server 2008. But people had to seek out the update and apply it, whereas in Windows 7 the new behaviour was the default.
By including the update in the latest round of patches send out via Windows Update on Tuesday, however, Microsoft made it marginally easier for users to find and much easier for enterprises to install. Applying the "important, non-security update" automatically makes the necessary changes for Windows XP users and others, wrote Adam Shostack, a program manager working in Microsoft's Trustworthy Computing section, on Tuesday.
Windows XP users who want the extra protection must select "Custom" rather than "Express" when Microsoft Update launches, then select optional software updates, and finally click on "Update for Windows XP". The (initially hidden) description for that update invites them to "Install this update to restrict AutoRun entries in the AutoPlay dialog to only CD and DVD drives. After you install this item, you may have to restart your computer."
In a separate blog post, Holly Stewart of Microsoft's Malware Protection Center wrote that the changes to Windows 7 appear to have reduced the risk for those users.
"Windows XP users were nearly 10 times as likely to get infected by one of these worms in comparison to Windows 7," Stewart wrote. "Although causative proof is difficult to quantify, it is quite possible that these figures reflect, at least in part, the improvements made to the security of autorun in Windows 7."
Shostack wrote that the changes won't affect "shiny media" such as CDs and DVDs that have autorun files. "We are aware that someone could write malware to take advantage of that, but we haven't seen it in the wild," he wrote.
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