Mac users may be surprised that versions of Apple's latest operating system, Snow Leopard, also installs an older version of Adobe System's Flash player, potentially putting them at a higher security risk.

The "initial" release of OS X 10.6 includes an earlier Flash player version than the latest version, which is 10.0.32.18, according to an Adobe blog post on Wednesday.

Upgrading to Snow Leopard, which was released on Friday, will actually downgrade the latest Flash player to version 10.0.23.1, which is not patched against some security problems, wrote Graham Cluley, senior technology consultant for Sophos.

That's problematic, as vulnerabilities in Adobe applications are frequently used by hackers in order to gain control over a PC. As operating systems have become harder to exploit, hackers have turned their attention to probing third-party applications.

Adobe's programs are an attractive target. Millions upon millions of computers worldwide have Flash Player, as well as other products as Acrobat and Reader, used for PDF (Portable Document Format) files.

Hackers have found ways to create malicious PDF documents that exploit a vulnerability when opened. The problems became so severe and so frequent that Adobe introduced a quarterly patching schedule for Acrobat and Reader, timed to coincide with Microsoft's patch releases on the second Tuesday of the month.

Flash Player isn't on that schedule, however. In July alone, Adobe issued 12 patches for the Flash Player. At least 10 of the vulnerabilities could allow an attacker to execute arbitrary code on a machine.

Adobe's Flash Player is a bit different than other applications in that its "Settings Manager," which is used to control security, privacy and other parameters, must be accessed through Adobe's Web site.

Through the Settings Manager, users can set how frequently Flash checks for an update, such as at seven, 14, 30 or 60-day intervals. The default interval is every 30 days. Adobe also has an online tool that confirms the version of Flash a computer is running.

Apple representatives contacted in London did not have an immediate comment.

The Flash player snafu comes as Apple has sought to build more protection into its OS, adding basic detection into Snow Leopard of two Trojan Horse programs called "RSPlug.a" and "Iservice".