Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool reads the following registry entry to determine the value for ScanningThreads:


The ScanningThreads registry value represents the maximum number of Virus Scanning API (VSAPI) threads that are allocated for scanning.

The Exchange Server Analyzer also reads the following registry entry to determine whether VSAPI message scanning is enabled:


A value of 1 for Enabled indicates that VSAPI scanning is enabled. A value of 0 indicates VSAPI scanning is not enabled.

Additionally, the Exchange Server Analyzer queries the Win32_ComputerSystem Microsoft Windows® Management Instrumentation (WMI) class to determine the value set for the NumberOfProcessors key. This value represents the number of processors installed on the computer, and it includes both physical processors and logical processors. Using Hyper-Threading technology from Intel, a physical processor can be split into two logical processors.

If the Exchange Server Analyzer finds that the value for ScanningThreads is less than (2 × NumberOfProcessors) + 1 on an Exchange Server computer that has VSAPI scanning enabled, a warning is displayed. The optimal value for ScanningThreads is equal to (2 × NumberOfProcessors) + 1. For example, on an Exchange Server computer with two processors, the optimal value for ScanningThreads is 5.

If Hyper-Threading is enabled, the value for NumberOfProcessors will be double the number of physical processors. It is recommended that you check with your antivirus software manufacturer to determine if physical or logical processors should be used in the above formula.
This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore the registry if a problem occurs. For information about how to restore the registry, view the "Restore the Registry" Help topic in Regedit.exe or Regedt32.exe.

To correct this warning

  1. Open a registry editor, such as Regedit.exe or Regedt32.exe.

  2. Navigate to: HKLM\System\CurrentControlSet\Services\MSExchangeIS\VirusScan

  3. In the right pane, double-click ScanningThreads.

  4. Enter the value returned from the above formula.

  5. Close the registry editor, and then restart the Microsoft Exchange Information Store service for the change to take effect.

Before you edit the registry, and for information about how to edit the registry, see the Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (

For more information about Hyper-Threading technology, see the Intel Web site (

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