Preface: I am not a Mac owner/operator.
Mac enjoys a more favorable position with regards to Security, for a variety of reasons:
Mac is a relatively secure system.
Mac makes a relatively prompt and active effort to keep the OS updated.
Mac occupies a smaller target profile due to the smaller number of Mac machines online.
Still, Mac users who use Microsoft Office and other third-party applications are vulnerable to exploits through those softwares.
And Mac users are no less vulnerable to the largest single vector for exploit…. that of Social Engineering exploit.
Additionally, Mac owner/users can themselves become a Vector for spreading Malware through forwarding email attachments to others with PC/MS systems.
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So What to Do?
Keep your Mac OS updated!
http://www.apple.com/macosx/features/security/
http://www.apple.com/support/security/
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to the best of my knowledge there is no AntiSpyware Utility for Mac.
Therefore you must increase your own awareness of Social Vectoring, such that you do not fall prey to phishing, and other too-good-to-be-true or dire-warning scams. Downloading and opening or worse- forwarding unknown email attachment content should always be avoided!
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to the best of my knowledge there is no "realtime" protection AntiVirus features for Mac.
But there is an excellent Virus Scanning utility (you already mentioned it) clamXav
http://www.clamxav.com/
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Keep your MS Office and/or other application softwares updated at all times.
Application software manufacturers realize their software may be vulnerable and issue updates on regular basis to insure best practice and best possible security.
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Read up on your Mac Operating System….. keep current.
http://www.macgeekery.com/tips/security/ba…c_os_x_security
http://www.securemac.com/macosxsecurity.php
Google is your friend for finding additional resources for Mac and Security.
Norton has some utilities for Mac Users
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Finally, Put your machine(s) behind a Router.
Today's modern Routers all have NAT built in hardware Firewalls and have WEP (less strong) and WPA (very strong) encryption and password access features.
Welcome to TomCoyote.
I'm glad you decided to become a Member.
And I'm glad to reply to your questions even though my experience base has a hard time rising to the occasion.
Best Regards
Doug