Adobe posted a new version of Flash on Thursday that addresses a critical security issue, (CVE-2010-0186) which "could subvert the domain sandbox and make unauthorized cross-domain requests." The new version, 10.0.45.2 replaces version 10.0.42.34.
Go to this Adobe page to see which version you have installed and to see the latest version, as well as find a link to the download page. You will download an installer: Adobe Flash Player.pkg.
Partial screen shot of Flash about page
Because there is no automatic update mechanism supplied by Adobe for stand alone Flash, users must become aware of these alerts and manually apply the update.