So... First and foremost you did a stupid thing, you bought a Mac Product! (not that Windows 8.1 is better, I despise it on my Laptop, which is why my main computer runs Win 7 until I find out how to obliterate that horrid Metro UI 100% from the computer and not just a stupid fake start button program... So yeah, no love for Mac and not much more for Windows these days...)
Now that I have that off my chest, you have infected you Mac with some Malware, Virus, and/or distasteful little bugger. Yes, Macs get infected; no they are not invulnerable to disease as many Mac lovers try to vehemently defend. The reality is that they have been getting bugs for over half a decade now (I had a key logger steal log in information for my email about 5 years ago, which is when I started learning more about how very false the "safe Mac" Propaganda is... thankfully they didn't get my bank account info.) The reason is because with the unfortunate surge in popularity of products like the iPhone and iPad, Black Hats and other distasteful programmers have been coding for Mac OS more regularly. Its basically a Supply and Demand deal, the demand for more Mac Products has gone up and they are more common, so now the guys who make Malware, Spyware, Viruses, and other nasty Software Bugs are justified in spending the man hours to program for it.
I would do what the link says and get some good solid software protection for your Mac, AVG is a good program I use on my own computers. Their free version is pretty good if you don't want to spend the money on a license, it just doesn't have the extra protection features beyond scanning & cleaning. I would also recommend you try and avoid those websites unless you do some research and learn how to root out nasty bugs like that, some of them somehow manage to live even after you do a full re-install (had it happen once, was very frustrating.) I would also try and use something like Google Chrome for web surfing or even FireFox (used it in place of Safari on my old Macbook) as they seem to do better about rooting out those bugs before they latch on, or at the very least warning you ahead of time.
