Microsoft Windows is prone to a vulnerability that lets attackers execute arbitrary code. An attacker can exploit this issue by enticing a legitimate user to use the vulnerable system to open a file from a network share location that contains a specially crafted Dynamic Link Library (DLL) file.
Block external access at the network boundary, unless external parties require service.
If global access isn't needed, filter access to the affected computer at the network boundary. Restricting access to only trusted computers and networks might greatly reduce the likelihood of successful exploits.
Run all software as a nonprivileged user with minimal access rights.
To reduce the impact of latent vulnerabilities, always run nonadministrative software as an unprivileged user with minimal access rights.
Do not accept or execute files from untrusted or unknown sources.
To reduce the likelihood of successful exploits, do not open or handle files from unknown or untrusted locations.
Do not follow links provided by unknown or untrusted sources.
Never follow links provided by unfamiliar or untrusted sources or visit sites of questionable integrity.
Microsoft has released an advisory and fixes. Please see the references for details.