This indicates an attack attempt against a vulnerability in Microsoft Windows Explorer.
The vulnerability is caused by an error when the vulnerable software handles malicious parameters in "search-ms://". It could allow a remote attacker to execute arbitrary code by constructing a malicious web page including a call to the search-ms protocol handler.
Windows Vista Service Pack 1
Windows Vista x64 Edition
Windows Vista x64 Edition Service Pack 1
Windows Server 2008 for 32-bit Systems
Windows Server 2008 for x64-based Systems
Windows Server 2008 for Itanium-based Systems
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the patch, available from the web site: