According to a new study by security vendor Symantec, the number of vulnerabilities identified in Apple's Safari browser in the first half of 2006 doubled over the prior six months—and it increased its window of exposure to Net-based exploits from zero days to five.

Microsoft's Internet Explorer browser still has a longer window of exposure—the time between when code exploiting a vulnerability appears and when a fix is available—and a greater total number of security holes. But Apple "is headed in the opposite direction" with respect to its browser's vulnerability to Internet-based threats, says Dave Cole, director of Symantec's Security Response team.