Adobe Acrobat release notes:

"Because PDFs are used so universally, they can be a target for hackers. Adobe provides regular updates to safeguard your computer from attacks."

What they really mean:

"Because we took a perfectly-safe document-formatting system and crufted it up with Flash and JavaScript and anything else we could think of, downloading a PDF file is about as smart as blowing a junkie in a third-world shantytown. Have a placebo and come see us again next month."