Microsoft has released an out-of-band patch to fix a vulnerability in how Windows handles shortcuts.
It affected supported versions of Windows XP, Vista, Windows 7, Windows Server 2008 and Windows Server 2008 R2.
Christopher Budd, senior security response communications manager at Microsoft, said in a blog post that "several families of malware have attempted to attack this vulnerability".
In particular from the "highly virulent strain" of Sality, said Holly Stewart from Microsoft's Malware Protection Centre.
"This family was known to infect other files - making full removal after infection challenging - copy itself to removable media, disable security, and then download other malware.
"It is also a very large family, one of the most prevalent families this year."
Microsoft saw an increase in attempts to exploit the vulnerability before releasing the patch.
For customers using automatic updates, it will apply once it is released but others should download, test and deploy this update as soon as possible.
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