OS X 10.6.6 update adds Mac App Store to OS X. Apple hopes success of the App Store’s success will carry over to the Mac platform. Apple vet apps according to some very strict rules, it also takes much of the risk out of the process. Many popular, serious and widely-used Mac applications will likely fall foul of Apple’s strict criteria. Pirated apps are also likely to fall under the rules. Anti-virus tools will be limited to performing on-demand scans of files and folders that you can access.”]
Source: https://nakedsecurity.sophos.com/2011/01/07/will-mac-app-store-keep-malware-out/