Is it true that Sophos disables OS X's built-in anti-malware scanner?

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scottj wrote:
It's been alleged to me that by running Sophos Anti-Virus on my Mac I have disabled the anti-malware scanner that was introduced in Snow Leopard [cf., www.zdnet.com/.../4104]. Is this true? Does installing Sophos Anti-Virus circumvent or disable any of OS X's built-in security provisions?

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Short answer: no.

Longer answer: OS X does not and has never had an anti-malware scanner.  What it does have is a select list of prevalent malware "fingerprints" that is checked during certain operations performed by the OS, such as downloading via Safari or Firefox, or saving an attachment from Mail.app.

Because of this, Sophos Anti-Virus for Mac could in some circumstances "pre-empt" the OS functionality via its on-access component by detecting the malware before the OS feature does.  However, the OS functionality is still there; it just wouldn't get the chance to detect the malware.

Sophos Anti-Virus includes a traditional "scanner" portion where you can do an initial scan or a manual clean-up scan of your storage devices, and also an "on-access" component that scans a file for malicious signs whenever the file is accessed.  Neither component (nor the installer) actively disables any security features already installed on your computer -- although we do recommend that you not run multiple on-access scanners by different vendors at the same time.  Since Apple doesn't provide true on-access scanning, its malware detection system coexists nicely with Sophos Anti-Virus.