Researchers at the FireEye security laboratory have identified a “zero day” exploit in PDFs which when opened in Adobe’s Reader can do malicious things. Once the PDF is opened in Adobe Reader it deletes a couple of key files on Windows machines (DLLs) and installs a couple of it’s own. Once those files are installed your computer connects to a remote computer and you have now become vulnerable to all types of malice.
For many years I have used the FoxIT reader. It looks similar to the Adobe Reader but performs, in the opinion of most, much better – faster – and in cases like this more secure.