Can I install CA Etrust AntiVirus Exchange Option on my Exchange 2

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I am thinking about putting a local virus scanner on my Exchange 2003 server.
I am currently running Exchange 2003 on a Windows 2003 server. I would be
installing Computer Associates Etrust AntiVirus 7.1 Exchange Option.

I have heard a lot of horror stories about this causing problems, even
corrupting your exchange server. A lot of sites actually do not recommend
it, but why would Etrust put out a product like this then? I would like
information as to what directories to exclude from scanning and just any
information as to how to install a antivirus program on an exchange server.

Any help would be grealty appreciated.

Thanks
.