Reports from the various malware researchers indicate that the exploit for Adobe PDF files is becoming widespread. Although it’s not clear at this time the exact distribution, there appears to be distribution via PDF links in banner ads, and also through the usual spam mail.
Adobe has an update available. To install, start up your Adobe program (reader or ‘writer’), and use Help, Check for updates. Current version is 8.12 (shown via Help, About). Any prior versions (before version 8) should be replaced with version 8.12.