They got your computer fixed but they have compromised your system. They'll steal any Vital Information they can get such as Usernames, Passwords, Banking and Credit Card Information. They'll watch every keystroke your computer does and Monitor everything you do. If you receive that type of message again just bring up your Task Manager and close the Browser Windows if that can't be done just use the Power Button and Shut the Computer down and Restart from a Cold Boot.
If you know how to Format a Hard Drive and Clean Install your Operating System that would be your best option. The Unconditional Formatting is the way to rid of it.A Quick Format only rids of the first and last parts of a Hard drive still leaving Vital Information accessible using certain Software's for Recovery purposes.
If you don't know how to do it then you'll need to take it to a Computer Tech to get rid of what was installed on your computer and have a clean O/S installed. Leaving it as is will be one major headache you won't need.