"Today," he adds, "PDFs are inherently more dangerous, in my opinion, than executables because you're lulled into thinking you're just looking at a document that has some text. You may be reading some text, but behind the scenes it's really doing whatever an attacker wants."

Adobe recommends that Windows, Macintosh and Linux users of Flash Player 11.2.202.233 or earlier, upgrade to the latest version of the program immediately.

The same should be done by users of Android 4.x using Flash Player 11.1.115.7 and Android 2.x and 3.x using version 11.1.111.8 of the software.

If you're not sure what version of Flash Player you're running, Adobe has a that will automatically give you that information when you visit it.

Users of Google's Chrome browser don't have to worry about upgrading their Flash Players because updates are pushed to that software behind the scenes automatically.