I am looking into buying a Blackberry. This may be a dumb question, but what about antivirus software for the blackberry?

Protect your computer and network, don't worry about the Blackberry.
You may want to not leave the device "discoverable" in the Bluetooth settings if you are going to be in public, but no know virus has attacked Blackberrys before. If/when it happens, software to protect will be available. I won't waste money on any software now.

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Enjoying carrying only one communications device for all...

I have offered several times in the past to write AV software for the BlackBerry. Since it does not run Windows or Office, those viruses do not affect it. My offer still stands. I will write the AV software, which will do nothing, and not even charge very much for it.

Sounds like a good deal to me