Microsoft Internet Explorer 5.01 SP4 on Windows 2000 SP4; 6 SP1 on Windows 2000 SP4; 6 and 7 on Windows XP SP2, or Windows Server 2003 SP1 or SP2; and possibly 7 on Windows Vista does not properly "instantiate certain COM objects as ActiveX controls," which allows remote attackers to execute arbitrary code via a crafted COM object from chtskdic.dll.