Several security companies are urging Windows managers to install the latest Microsoft Exchange Server patch, despite reports that the fix is causing problems for some mobile devices. “This is a critical flaw and administrators should test and install the patch as soon as possible,” said David Litchfield, a U.K.-based security consultant with Next Generation Security (NGS) Software Ltd. “Until the patch is installed, administrators should consider blocking or quarantining calendar-based mail messages as an interim solution.”