Yay Services YAY Services ripoff Internet

 I was working for my classes on my computer and a  full screen pop-up took over my screen. The message said that my computer has been hacked and I must call this number 877-667-7972 to remove it. The people who answered sounded like people from India, but said to be in Salt Lake City. They communicated my PC had a virus destroying everything , but they could remove it for $499, to a maximun of 3 computers for 1 year. I took them 3 hours to fix it, so I decided to call them other day for the other computers. One month after the same problem appeared but neighther the phone number they gave or the e-mail address  worked, another pop-up like a chat format showed up with another phone nuber to call. I won't ever call any of those anymore. How can these types of thieves work so easily???