OSX/FkCodecA is Adware disguised as a "Video Codec" necessary to watch online videos. When the user attempts to watch a video on a shady site, they are prompted to download and install the codec first. The codec installer prompts the user to install browser extensions and new search homepages as part of the regular install process (defaulted on). Upon acceptance, these Potentially Unwanted Programs (PUPs) will serve ads and collect user information from the browser [1].

References:

1. http://www.thesafemac.com/osxfkcodec-a-in-action/