The SANS Institute on Monday updated its Top 20 list of Internet vulnerabilities, noting "rapid growth in critical vulnerabilities in Mac OS X, including a zero-day vulnerability." The security firm acknowledged that the operating system "still remains safer than Windows, but its reputation for offering a bullet-proof alternative is in tatters."

SANS defines a zero-day vulnerability as one that "causes damage to users even before the vendor makes a patch available." In the case of Mac OS X, Safari was susceptible to a flaw that automatically downloaded and executed a malicious file simply by browsing to a specific Web site. Apple fixed it, "but almost immediately had to issue a second patch to stop another attack involving email attachments," according to the SANS report.

SANS noted: "As attackers are increasingly turning their attention to the platform, OS/X vulnerabilities are being discovered at a rapid pace, which could erode this safety in the future."

Apple wasnit alone in getting dinged for critical vulnerabilities, however. SANS also pointed to "continuing discovery of multiple zero-day vulnerabilities in Internet Explorer," as well as "rapid growth in critical Firefox and Mozilla vulnerabilities." File-based attacks, especially those involving media and image files as well as Microsoft Excel documents, continue to surge too.

On the positive side, SANS also saw "substantial decline in the number of critical vulnerabilities in Windows Services," although trend turned into a wash for Microsoft because of the other problems documented by the firm.