Best Practices - SharePoint Anti-virus scanning exclusions!!!

Occasionally different anti-virus products can interfere with SharePoint operations. The following is a list of suggested locations to exclude from your AV scanner. Remember, this is merely a suggestion, so use at your own risk!

1.  %PROGRAM FILES%\Common Files\Microsoft Shared\web server extensions\12
2.  %WINNT%\temp
3.  %PROGRAM FILES%\Microsoft Office Server
4.  %WINNT%\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\
5.  Documents and Settings\All Users\Application Data\Microsoft\SharePoint\Config\     (the config cache)
6.  %WINNT%\Temp\WebTempDir

UPDATE: We've released a KB that covers this.
http://support.microsoft.com/kb/952167

But is you want to SCAN uploading and downloading of documents in SharePoint, You need to configure Antivirus in Central Administration > Operations > Security Configuration and Select Antivirus.

NOTE: You can activate Antivirus measures only after installing a compatible Antivirus scanner. In a server farm, you must install Antivirus software on every Web front-end server in the server farm.

To enable Antivirus Settings section, Select one or all of the following:

1. Scan documents on upload.
2. Scan documents on download.
3. Allow users to download infected documents.
4. Attempt to clean infected documents.
5. In the Time out scanning after ___ seconds box, type the number of seconds to allow before timing out the scanning process.

NOTE: The default time is 300 seconds, or 5 minutes. This should be enough time to allow the Antivirus processes to finish without affecting performance. The default time is recommended, but you can adjust this time if you are experiencing performance issues.

6. In the Allow scanner to use up to ___ threads box, type the number of threads to allow the scanning process to take up.

NOTE: By default, the number of threads is set to 5, which should be sufficient for even a large number of sites. The default number of threads is recommended, but you can adjust the number of threads if you are experiencing performance issues.

7. Click OK.
   
   
   NOTE: Best Practice is to No need to scan for documents which are getting download from 

   SharePoint, but please note it totally depends upon your business need.