Adobe has released a bulletin related to critical flaws in Reader and Acrobat. The details are not fully disclosed but Secunia, a security research company, does discuss a boundary error related to certain types of content in PDF's. It is possible that this boundary error can be exploited, code can be executed and privileges compromised. Many researchers believe that the other validation errors are simular in nature and delivery. This is a platform independent issue so Windows users are also affected.
Users have to download a PDF and view it which gets back to a bigger issue, that users should only open files from users that they know or from sites that are trusted. It is important that users update their Acrobat or Reader application to the latest versions.