I've been using Adobe Reader for many many years now, stretching as far back as when it was called Acrobat Reader. Adobe has continued to update it's reader and is currently up to version 9. To most people though, the functions of the reader they use have changed very little. For few more advanced users, who use all of the extra features of Adobe Acrobat to make PDFs then you probably have enjoyed the additions Adobe has made over the years, but regardless of whether you use them or not, they're making the PDF reader more insecure (and bloaty at the same time, Adobe have it auto load in the background when you turn on the computer because otherwise it would be too slow to load when you opened a document).
If you didn't know it already, apart from displaying text and pictures PDF documents can do other things if you use the newer versions of Adobe Reader. They can execute JavaScript commands and also execute attachments that have been inserted into the PDF. Using these functions (which should never have been put into a PDF reader in my opinion), people who wish to create malicious PDF files, put them on websites and then when your browser goes to view them using the Adobe PDF plugin that allows you to read PDFs from within your browser - execute code and you have yourself a virus.
You can help protect yourself in a number of different ways. The best way is to boycott Adobe Reader and move to a PDF reader which I use which is extremely basic - called Sumarta PDF Viewer ( http://blog.kowalczyk.info/software/sumatrapdf/index.html) and it's less likely to be affected by all these issues. It won't view PDFs in your web browser, so you have to download them to read them, but it's a small price to pay for security. Sadly FoxIt PDF Reader also has the insecure technology built into it.
If you still must use Adobe Reader, either for convenience or because something does depend on more advanced features like commenting etc, then follow these steps to at least disable the stuff which can be used to mount an attack.
1. Open Adobe Reader
2. Choose Edit, Preferences
3. Click On The JavaScript Tab and Uncheck "Enable Acrobat Javascript"
4. Click On The Trust Manager Tab and Uncheck "Allow Opening of Non-PDF File Attachments With External Applications" and then Click OK
You now have secured Adobe Reader as much as you can. Be careful about what sites you visit and make sure you keep Adobe Reader up to date.
