A security flaw in an operating system is dangerous, but a security flaw that's being actively exploited in the wild, and for which there is no official fix, is much more problematic.

That's exactly what's happening to Apple's latest version of OS X, according to security company Malwarebytes. An OS X security flaw detailed in July by security researcher Stefan Esser allows an attacker to install software on a user's computer without permission or password. Now, Malwarebytes researcher Thomas Reed has encountered an exploit that takes advantage of this flaw, installing VSearch and Genieo adware as well as MacKeeper junkware — in short, software that you don't want on your computer, ever.