Mac users should think twice before downloading PDFs of uncertain origin: A new bit of spyware — under the guise "RecentNews.ppa.pdf" — is actually a nasty piece of malware that shrouds itself in a clever text-reversing trick.

Although compromised PDFs do exist, it's much easier to spread malware through an executable application. Backdoor:Python/Janicab.A spreads itself through an app that's easily mistaken for a harmless PDF document, according to a report from the Finnish security gurus at F-Secure Labs.