The new feature behaves a cross between a traditional antivirus tool and the “Are you sure you want to open this?” warnings already present in Leopard. I doubt it’s doing any real-time heuristic scanning and it’s definitely not running as a visible app in the OS, but if it’s checking .PKG and .DMG files for malware before you run or mount them, well, that sounds an awful lot like what your average Symantec, AVG or Kapersky product is intended to do.
The first report came from The Mac Security Blog, and it’s been corroborated by Snow Leopard testers over at the MacRumors forums. We’ll try to test this one out as best we can, but it’s looking like Apple may have slipped this slightly unflattering feature into their new OS, stealth-style. [The Mac Security Blog, MacRumors]