From Adobe’s recent security advisory, last updated on 31 July 2009:

A critical vulnerability exists in the current versions of Flash Player (v9.0.159.0 and v10.0.22.87) for Windows, Macintosh and Linux operating systems, and the authplay.dll component that ships with Adobe Reader and Acrobat v9.x for Windows, Macintosh and UNIX operating systems. This vulnerability (CVE-2009-1862) could cause a crash and potentially allow an attacker to take control of the affected system. There are reports that this vulnerability is being actively exploited in the wild via limited, targeted attacks against Adobe Reader v9 on Windows.

Adobe is considering this a critical update, considering that an unpatched computer could be taken over.

To Patch
Check the “Solution” section of Adobe’s Security Bulletin for specific download links for updated versions Flash Player, AIR, Acrobat and Reader software.

NOTE 1: If you are using Internet Explorer AND another, plug-in based browser (such as Firefox or Opera), run the “About Flash” check for each browser.

NOTE 2: Internet Explorer users, if you upgrade the Flash Player, by default, you will be prompted to install the Google toolbar, bu you may uncheck this option.