A new threat spreads currently on Apple's Mac OS X operating system. The Russian security firm "Dr.Web" has dubbed the software "Trojan.Yontoo.1". As the name implies, the Trojan modifies the operation of an affected computer. The malware sneaks through fake movie-trailer-sites onto your Mac. The maleware then generates ads on legitimate sites where they are not supposed to be. Thus revenue for the Trojan is being created.
There are several entry points for the pest: either as a free down-loadable media player (you get the "friendly reminder" your Flashplayer is allegedly outdated ;-)), or sometimes it claims to be a "quality improvement" software, a "download accelerator" for video playback. (You don't need such nonsense on your MAC!)
However, in reality the promised applications you just install a plug-in for the browsers Safari, Chrome and Firefox which is responsible for all the many more ads you'll suddenly see on the website you visit...
The Trojan does not only bring its creators sales, but also information about your surfing habits once your MAC is affected. The trojan is recordeding your surfing activities. This thing was found on Mac OS X, but a variant should also exist for Windows PCs as it just need a DOS patch attached.