Danger, Will Robinson! Adobe is warning that "critical vulnerabilities" have been found in Adobe Reader and Acrobat 8.1.1 and earlier. They are recommending that Acrobat 8 and Adobe Reader users install the 8.1.2 update as soon as possible. Those who are using Acrobat 7 are advised to install the 7.1.0 update quickly as well.
A full summary of the security concerns and links to the update files can be yours by visiting the Adobe security update site. Note that while Acrobat & Reader 8.1.2 have been out for some time, the 7.1 update is fresh this week and the security issue is newly disclosed.