A serious flaw in the way Mac OS X handles downloaded files with fake file extensions could allow attackers to install malicious code on Apple computers, writes CNET. The defect is the third security problem revealed within one week. Mac's Safari browser could allow the downloading of malware. "This could be really bad," the SANS Internet Storm Center, which tracks network threats, said Tuesday. Apple is developing a patch for the flaw, according to a company rep.

There are no known attacks that take advantage of the flaw, but "the skill level required to exploit it is very low. Pretty much anyone can do it," according to Alfred Huger, senior director of engineering at Symantec. "If you have a Mac and use Safari, it is something you should remediate immediately," he said.

Mac OS X users can protect themselves by disabling the "Open safe files after downloading" option in Safari.