Never, ever, ever, ever install a 'required plug-in' that a random web site tries to 'give you.'

[onehandle]

I think Mac people are mostly smart about this, but case in point...

Yontoo spoofs an Apple dialogue box used to seek permission to install a program. "After clicking on 'Install the plug-in, the user is redirected to another site from which Trojan.Yontoo.1 is downloaded," Dr Web says.

Fraudsters have rigged movie trailer pages that contain a prompt encouraging users to install a plugin needed to view the content. However, granting permission merely installs the Yontoo plugin.

"Yontoo has also been deceptively packaged as a media player, video enhancement software and a download accelerator, including an offer to install "Free Twit Tube", which again installs Yontoo. Once installed, it displays ads that would not otherwise appear," Dr Web says.

Not all antivirus companies are classifying Yontoo as a trojan, however. Symantec assessed the Windows version of Yontoo as "potentially unwanted software". On Windows, the plugin installs a browser extension displaying advertisements that appeared to come from Facebook, Symantec said.

http://www.zdnet.com/is-the-new-mac-trojan-hitting-os-x-browsers-really-a-trojan-7000012937