Apple Says OS X Vulnerable to Security Breach SEATTLE (Reuters) - Apple Computer Inc., long considered to be relatively immune to the security holes and viruses that plague longtime rival Microsoft Corp.'s Windows, said on Friday a security hole in its software leaves users' computers vulnerable to attack. Apple, warning of a rare security hole in the company's OS X operating system for the second time this month, said in a release that a "theoretical vulnerability" in an application used to get help while browsing the Web could expose users to a malicious software code. The specific nature of the security hole, such as whether it makes the computer vulnerable to outsiders or allows virus-like code to enter the operating system, was not made clear. Cupertino, California-based Apple's officials declined to provide specific comment beyond the release. Mac, and its legion of enthusiastic users, have long touted the benefits of owning Apple's Macintosh personal computer, such as its ease of use and immunity from the computer viruses that plague users of PCs running Microsoft's Windows operating system. Apple urged users to go to its Web site http://www.apple.com/support/downloads/ to download a free software update. Microsoft, whose Windows market share of over 90 percent makes it an attractive target for virus writers and attackers, has been plagued with crippling security holes and malicious software exploiting them. "While no operating system can be completely immune from all security issues, Mac OS X's UNIX-based architecture has so far turned out to be much better than most," said Philip Schiller, Apple's senior vice president of Worldwide Product Marketing. Apple says that OS X, which is based on a software system called Unix that is more than two decades old, is more robust because it is built with better permissioning tools and also draws upon the expertise of other software developers who write programs based on Unix. Steve Jobs, Apple's co-founder and chief executive, likes to take the stage to tell loyal users of the company's "insanely great" products with "the best operating system in the world" but the message from company officials on Friday was markedly toned down. "Apple takes security very seriously and works quickly to address potential threats as we learn of them-in this case, before there was any actual risk to our customers," said Schiller.