Microsoft is to release security patches for Internet Explorer and Visual Studio this week.
The Internet Explorer patch has earned Microsoft's most serious ranking of "critical" and the one for Visual Studio is "serious".
Microsoft said it planned to release the patches on Tuesday 28 July, but could give no specifics about the issue prior to release.
An advance advisory said the Visual Studio bulletin will address an issue that can affect certain types of applications.
The IE bulletin will provide defense-in-depth changes to the browser to help provide additional protections for the issues addressed by the Visual Studio bulletin.
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"The Internet Explorer update will also address vulnerabilities rated as critical that are unrelated to the Visual Studio bulletin that were privately and responsibly reported," the advisory said.
The threats affect IE 6, 7 and 8, Visual Studio .NET 2003, Visual Studio 2005 and 2008 and Visual C++ 2005, 2008.