This upcoming MacDefender patch is not the first time Apple has tweaked Mac OS X in response to a malware threat. Many people forgot that recent versions of OS X were designed with a built-in malware detection system. Mac OS X 10.4 and 10.5 Leopard had a validation system called File Quarantine. In Leopard, it triggered a warning dialog box when you opened a file that was downloaded from your browser, email client or iChat. OS X 10.6 Snow Leopard improved upon File Quarantine by adding a system to check files against known malware definitions. These definitions were stored in the XProtect.plist file.
Just last year,
