The next time someone sends you an email with a PDF attachment, take a moment before clicking to open it. While most PDF files are benign, hackers have recently been using PDFs in new and very lethal ways. Malicious PDFs are nothing new. In my post for Avast’s blog here, I explain their history and how two news items have shown that they are still an active threat vector and being exploited in new and interesting ways, such as this invoice which has different amount due items depending on the particular reader used to view the file.