Well, one, at least. In the Apple anti-malware feature that we discussed back in September, there were two types of malware in the system's definitions. With the latest update to Mac OS X 10.6.4, Apple added another bit of malware to these definitions: the HellRTS backdoor that Intego discovered in April 2010.
So Apple's anti-malware feature now protects against three types of malware. Intego's VirusBarrier X6 protects against all known Mac malware.