zCodec is a Trojan

"It is known as adware/ZCodec or Adware/EMediacodec and affects most versions of Windows. Some of the files that the adware has been downloading are particularly nasty, including a rootkit called Ruins.MB, which does what it says on the tin."
SECURITY OUTFIT Panda software says that a video codec which is appearing in the wild offering "up to 40 percent better video quality" is a nasty bit of adware.